# Optimizing pressurized CO2



## geeks_15 (Dec 9, 2006)

I've been using pressurized CO2 for several years now with the same basic setup (inline diffuser, pH monitor shut off, CO2 running 24/7). I've read all kinds of internet opinions on the best way to set it up, so I was wondering if I could get some opinions from some of the planted tank minds on this forum.

Some people don't like pH monitors.
Some say turn CO2 off at night and some say leave it on always.
I've read stories of CO2 dumping where the last of the CO2 in a pressurized cylinder rapidly goes into the tank and kills the fish.

Is there a concensus or not? I haven't had any problems per se, but I've seen this come up on the forum and wanted to explore things a little.

Thanks,


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## bosmahe1 (May 14, 2005)

I don't believe there is a consensus at the moment. I think it falls in with the saying, "There's more than one way to skin a cat".

I've run co2 24/7 without a ph monitor, for several years. About a month ago I installed a solenoid to shut off the co2 at night. The co2 is on for 12 hours and the lights are on for 10 hours. Since the bubble rate is a little higher now (3 bps), I don't think the cost savings is going to be substantial. If you factor in the cost of the solenoid, the "return on investment" may be several years. But, I do like the fact that, I don't "feel" the need to check the drop checker, every single morning. Now I can wait till fish feeding time to check the drop checker. If it ain't yellow, I think I'm safe.

Has my plant growth or algae level changed any because of the change? Not that I can detect. So at this moment, I wouldn't be able to tell you one method was substantually better than the other. Whatever is more convenient for you. Since you have the PH monitor, I would use it. Just keep in mind buffering from phosphates will most likely alter PH, aside from co2 level. How much phosphate does it take to throw off the PH monitor? My guess would be an awful lot.

I really like this question by the way.


Henry


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## Philosophos (Mar 1, 2009)

I was just touching on the issue of controllers helping someone else out in PM, I feel what I said there applies to this thread:



> Personally I'd lose the pH controller. It's never great to hear, but it's the conclusion myself and many others have come to. You won't see top ranking tanks running pH controllers for the reasons I'm about to explain. You can ask Tom Barr to verify any of this for you, and I don't know of a bigger CO2 nut than him.
> 
> Less than 95% of the CO2 in your water column is not going to make it into your plants; it's all waste. This means your plants uptaking at a certain time of day isn't going to greatly effect your CO2 levels. In the day to day scheme of things, your tanks phosphate levels will change, ammonia may come up a little now and then, calibration may be lost, pH electrodes drift, plecos crap in funny places, and so on. All of these things can quite easily impact your tank more than CO2 will.


Now as for the night time break, I do that for the fish rather than the plants. The extra O2 does have some indirect benefits to plants and the tank as a whole, but it's mostly about the fish. How many of us keep schools of 20, 50 or 200 fish that cost us $3-5 each? What about proven pairs who's fry help us to pay for our hobby? As much time as I put into plants, the fauna is not something that disappear from my considerations.

Gas-offs suck; they're a good argument for quality equipment. I've had everything survive minor ones though, and I've found good surface disturbance (rippling not splashing) allows things to gas off faster. Faster gas-off means turning your CO2 up higher, but it also means far more steady CO2. Rather than culminating at the end of the day as happens with glass-like surfaces, the CO2 tends to stay noticeably more level from the time the lights go on until they shut off.

I hope this helps some. I'm sure there are those who would disagree.


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## Zapins (Jul 28, 2004)

I agree with the bit about pH controllers. I had one and found that it really didn't help at all. I think its mostly a marketing gimmic rather then an actually useful tool.

I also think the only argument for turning CO2 off at night is a high fish load. Since I have a low fish load, I leave my CO2 running 24/7 since the few fish that I do have don't use all the O2 at night.

I've never had an end of tank dump, strangely enough... or perhaps I have and I just never noticed. My fish are used to incredibly high CO2 levels, so perhaps a little more doesn't do much to slow down their little fishy tails??


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## bosmahe1 (May 14, 2005)

Yeah, I've never had more than about 35 fish (Tetras, Rasboras) at a time in a 46 gallon. That's not counting the RCS though. So running co2 24/7 has never been a problem for me. I've always kept plenty of surface movement. One thing that I've read is that high co2 levels in the water doesn't displace or reduce O2 in the water so, why do people imply that co2 should be shut off at night to allow for O2? Maybe some kind of interference with the gills? I've never had an EOTD with my Redsea Regulator, just an increase by a few PSI when it was near empty. I would adjust the working pressure down to the original PSI of when it was full, not such a big deal.


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## jestep (Nov 14, 2009)

This is my experience from keeping mixed plant/discus tanks. 

I don't recommend on-off/day-night CO2 schedules. The reason is because it can (does) cause huge PH swings every day. For plant only tanks, I'm sure it's fine but if you have anything as sensitive as a neon tetra, it generally causes a ton of stress if it doesn't kill the fish completely. 

I do add an airstone at night, but I leave the CO2 going on a controller. I think you would be fine without an airstone if you only inject a moderate amount of co2. If you keep a fairly high concentration of plants and CO2 going it can get out of hand when the lights go out and the plants stop using CO2. Something to create light degassing like an airstone is good because the ph stays relatively stable as the agitation takes the place of the plants during the day.

I've seen over 2.0 ph (6 - 8 ) swings from on-off co2, vs. just a tenth of a point or so from adding an airstone.

As to why I use a controller, I have hard water here with a virtually unlimited buffering ability, so CO2 poisoning is very possible. For soft water you would have a PH crash long before your fish were poisoned from excessive CO2, which is another reason to use a controller. If you have a low load or hardy fish, I could easily see not using one. With Discus and hard water, it's not a chance I will take.


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## geeks_15 (Dec 9, 2006)

Here is my argument for pH controllers.

They are a safety feature and they give you a rough idea of the amount of CO2 entering the tank. I set my pH target low, so the CO2 is nearly constantly running. There is no need to turn the CO2 off a night because you can't over do it. The pH monitor prevents it. I can also use it to monitor the CO2 entering the tank. For a while, I had a CO2 leak. I couldn't hear it or see it, but I knew there was one because the pH was not getting as low as normal. I tried a couple things and pH was still too high. Then I found the problem. I fixed it and the pH dropped back down to the normal range. Also, while getting my tank started I can slowly ramp up the CO2. I can slowly set the pH to a lower and lower level and assure that the fish are not being stressed. Maybe I'm too paranoid, but I've never lost a fish to CO2 poisoning. 

If your goal is to keep the pH at an arbitrary level then they work pretty well for that. The question is why keep the tank at any certain pH? I don't try to keep the tank at a certain pH, I try to keep a certain amount of CO2 in the tank and use the pH to monitor that and prevent over doing it. 

As for the accuracy of the pH monitor, mine has been very reliable. I've had mine for about 5 years and have only calibrated it a couple times. I occasionally test against known pH levels and test water with chemical pH tests and compare to the monitor read out. Mine has been accurate. At least as accurate as chemical pH tests. I use my monitor to test the pH of other tanks (bring a cup of water from the other tank and insert probe).


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## geeks_15 (Dec 9, 2006)

Regarding leaving CO2 on overnight:

My theory is that I leave the CO2 on, so that when the light comes on and the plants are ready to photosynthesize they are not limited by lack of CO2. Too much CO2 overnight is not a concern because I have the pH monitor.

A stable pH is also a possible benefit. I say possible because stability is often preached by fish keepers as a key to success. PH swings can be a lot as jestep says (BTW, you can watch the swing if you have a pH monitor). I'm not totally convinced this matters because pH swings naturally occur where there are aquatic plants. Diane Walsted discusses this in her book.

So I leave my CO2 on overnight. The worst that can happen is I waste some CO2. I say the worst because I have the pH monitor to prevent too much CO2.


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## bosmahe1 (May 14, 2005)

PH swings don't bother fish. It's changes in GH and TDS that fish would notice.


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## Philosophos (Mar 1, 2009)

geeks_15 said:


> My theory is that I leave the CO2 on, so that when the light comes on and the plants are ready to photosynthesize they are not limited by lack of CO2. Too much CO2 overnight is not a concern because I have the pH monitor.


Pressurized CO2 establishes quickly; 30 minutes to nonlimiting in most tanks, perhaps 60 in tanks around 200 gal.



geeks_15 said:


> A stable pH is also a possible benefit. I say possible because stability is often preached by fish keepers as a key to success. PH swings can be a lot as jestep says (BTW, you can watch the swing if you have a pH monitor). I'm not totally convinced this matters because pH swings naturally occur where there are aquatic plants. Diane Walsted discusses this in her book.


I've got a pH meter, and I've tested how much my pH swings. I've had it drop or increase by .5-.8ppm within an hour of lights on/off. Many other tanks do the same, and many (including my own) tanks have spawned sensitive fish under these conditions. I don't even see stress indicatiors when the CO2 kicks in once the fish are adapted to the tank.

Instead of looking to pH change sensitivity, try looking to KH.

In all reality, you're wasting over half your CO2 by running it during lights off. If anything it's stressing the fish.


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## bartoli (May 8, 2006)

I set up pressurized CO2 not for the plants, but to keep the pH low for the neon tetras. Thus, I use a pH monitor to control CO2. Low pH does make a big difference for the neon tetras.


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## Zapins (Jul 28, 2004)

Interesting opinions so far. I think this might be relevant to the discussion here (an explanation of what CO2 does in fish that are *not *accustomed to it).

http://www.aquaticplantcentral.com/...cussions/51508-ph-co2-fish-why-they-gasp.html


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## geeks_15 (Dec 9, 2006)

> In all reality, you're wasting over half your CO2 by running it during lights off. If anything it's stressing the fish.


Yep, that is what I said. At worst I'm wasting CO2. But the fish are not stressed, because the CO2 levels are roughly the same as they are during the daytime because of the pH monitor.

Also, I don't waste over half my CO2 because the pH monitor turns the CO2 off. I realize I said it is running almost all the time. I meant during day time hours it is running almost all the time.


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## geeks_15 (Dec 9, 2006)

> I set up pressurized CO2 not for the plants, but to keep the pH low for the neon tetras. Thus, I use a pH monitor to control CO2. Low pH does make a big difference for the neon tetras.


I'd be surprised if the neons benifit from pH lowered by CO2. Because it is kind of a false lowering of the pH as far as the fish is concerned. The H+ concentration is increased in the water, but I doubt fish respond much to that one change. In the neon's natural habitat the low pH is due to many factors acting together (low TDS/low kH/low GH, mulm, tannins, etc)

Perhaps just the H+ concentration has an effect. But it seems more likely that pH is a measure (a crude measure) of all the other factors which combine to raise the H+ concentration in the neon's natural habitat.


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## Philosophos (Mar 1, 2009)

geeks_15 said:


> Yep, that is what I said. At worst I'm wasting CO2. But the fish are not stressed, because the CO2 levels are roughly the same as they are during the daytime because of the pH monitor.
> 
> Also, I don't waste over half my CO2 because the pH monitor turns the CO2 off. I realize I said it is running almost all the time. I meant during day time hours it is running almost all the time.


But the pH alteration from CO2 doesn't stress fish; myself and countless others watch the CO2 turn on in the morning and go off in the evening without observing any indications of stress. If anything, if what Zapins is saying about hemoglobin and gill mucus is true, a break from CO2 during the off-hours should increase the O2 levels in the fish's bloodstream which is a far healthier thing. The O2 relationship with fish health and growth are well documented. His statements certainly match my somewhat more rudimentary understanding of acidosis.


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## geeks_15 (Dec 9, 2006)

Hmm, good point. Giving the fish a break from CO2 may be beneficial. That could be a reason to shut off CO2 at night. OK, maybe I'll go back to shutting off the CO2 at night and see how things go.

Have I convinced you to get a pH monitor yet Philosophos? Or at least not advise people to get rid of their pH monitors?


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## Philosophos (Mar 1, 2009)

geeks_15 said:


> Have I convinced you to get a pH monitor yet Philosophos? Or at least not advise people to get rid of their pH monitors?


Unfortunately I can't. Believe me, I would absolutely love to be able to keep CO2 levels fixed and automatically compensated for. I don't trust my drop checker to tell me if CO2 is okay all over the tank from one point of measurement, and I don't trust a pH meter not to drift when I'm not watching. I just can't see how combining the two would be a good idea.

Given a maximum change of .8 in pH from CO2 that I've observed, and the fact that a tank can fluctuate by .2 pH over a week without much trouble, having at least a 25% fluctuation of CO2 reading accuracy within a tank isn't acceptable. When I work with a bubble counter, I'm usually doing so within a margin of +/- 10% to fine tune injection and carefully observing my plants.

It's definitely nothing personal, but I can't figure a way that someone would be better off with pH regulator for CO2 control. If there's some good evidence for why it should work that mitigates my concerns, then I'd definitely be interested. If there's a way to make them work, I won't hesitate supporting their use; I just haven't seen it yet.


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## bartoli (May 8, 2006)

geeks_15 said:


> I'd be surprised if the neons benifit from pH lowered by CO2. Because it is kind of a false lowering of the pH as far as the fish is concerned. The H+ concentration is increased in the water, but I doubt fish respond much to that one change. In the neon's natural habitat the low pH is due to many factors acting together (low TDS/low kH/low GH, mulm, tannins, etc)


From time to time, I do read up on fish physiology. That led me to appreciate the health effect of pH level on fish. However, I have yet to come across a study on the so called "false" lowering of pH. Can you provide some kind of reference?



geeks_15 said:


> Perhaps just the H+ concentration has an effect.


That is my understanding. Regardless of how a certain pH was reached, ultimately what counts is the degree of hydrogen-ion concentration which started a chain of cascading physiological effects.


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## geeks_15 (Dec 9, 2006)

> Given a maximum change of .8 in pH from CO2 that I've observed, and the fact that a tank can fluctuate by .2 pH over a week without much trouble, having at least a 25% fluctuation of CO2 reading accuracy within a tank isn't acceptable. When I work with a bubble counter, I'm usually doing so within a margin of +/- 10% to fine tune injection and carefully observing my plants.


Hmmm, so how do you monitor CO2 levels? Just a bubble counter? Can you describe you CO2 setup?


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## geeks_15 (Dec 9, 2006)

> However, I have yet to come across a study on the so called "false" lowering of pH. Can you provide some kind of reference?


I must admit I'm just pontificating on this point. Perhaps you know better than me. Its just that although pH is a measure of H+ concentration, so much can affect the pH besides just the H+ concentration, and CO2 isn't usually a big factor in nature. I would think the whole mix would be more important the just H+ ions. But no, I don't have a reference. Do you have any recommended reading on fish physiology regarding H+. Most basic aquarium reading I have discusses pH very superficially.


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## Philosophos (Mar 1, 2009)

geeks_15 said:


> Hmmm, so how do you monitor CO2 levels? Just a bubble counter? Can you describe you CO2 setup?


I use a JBJ bubble counter and a drop checker. The BPS is something I restrict to CO2 adjustment on that tank at that time. I don't call 1bps the same between two tanks for CO2 levels, and I don't compare CO2 a month ago to CO2 today. Flow dinamics and CO2 retention changes. If I want to go up by 10%, I just take a bubble count and add 10%.

The drop checker is nice to get an overall level in the tanks at a glance. I can spot the color from across the room, and it tells me quite often when something isn't quite right. With a new tank or any altered flow, I'll move the drop checker around some to look for dead spots in order to improve distribution. After a while, I'll let the drop checker settle in one place and get to know what color it should be in that place at any given time of day. If the pattern changes, something else has changed.

Above all else, I watch the plants. 2-3 days of altered CO2 will show up quite clearly. Good in one area doesn't mean good in another, but the plants respond this way. With good fertilization, trouble shooting is about evenly spread light and CO2 most of the time. What a PAR and CO2 meter will tell you for hundreds or thousands, your plants will indicate to a lesser extent for free.


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## geeks_15 (Dec 9, 2006)

> I use a JBJ bubble counter and a drop checker. The BPS is something I restrict to CO2 adjustment on that tank at that time. I don't call 1bps the same between two tanks for CO2 levels, and I don't compare CO2 a month ago to CO2 today. Flow dinamics and CO2 retention changes. If I want to go up by 10%, I just take a bubble count and add 10%.


It sounds like we are doing pretty much the same thing. I just use the pH monitor and you use the drop checker as a tool to measure the CO2 concentration. (BTW, the pH monitor doesn't have to be stationary. You can move it around the tank like you do your drop checker)



> Given a maximum change of .8 in pH from CO2 that I've observed, and the fact that a tank can fluctuate by .2 pH over a week without much trouble, having at least a 25% fluctuation of CO2 reading accuracy within a tank isn't acceptable


My tap water pH is 7.8 and I can get it down to 6.1 with CO2 pretty quickly (maybe an hour or two), so my tank is obviously different in that regard. I'm not sure what you mean by 25% fluctuation, maybe you could explain that statement in a different way so I can understand.

I agree that just testing the pH won't tell you much. But using the pH monitor constantly and watching the changes that occur as the tank ages and you tweak different things, you can learn a lot and the pH monitor can give you good information. The main benefit of the pH monitor over a drop checker is that the pH monitor prevents rapid unchecked increases in CO2 that could harm the fish.


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## bartoli (May 8, 2006)

geeks_15 said:


> Its just that although pH is a measure of H+ concentration, so much can affect the pH besides just the H+ concentration


I am not sure of what you are saying. pH measures only the dissolved hydrogen ions (H+).

When a metric M claims to measure only X and yet there are things that affect M other than through X, then M is not a true measurement of X. Is that what you are saying?



geeks_15 said:


> Do you have any recommended reading on fish physiology regarding H+. Most basic aquarium reading I have discusses pH very superficially.


You may want to look into the book "The Physiology of Tropical Fishes":

http://www.amazon.com/Physiology-Tropical-Fishes-21-Fish/dp/0123504457


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## jestep (Nov 14, 2009)

I think the co2 superficial statement actually has some bearing. 

PH is the measurement of hydrogen ions, however, co2 only contributes to this via carbolic acid equalization. The deterioration of plant material contributes many more acids and compounds than just carbolic acid. I think this is a good argument against using co2 for proper water ph.

I disagree however, on saying that co2 changed ph doesn't have a affect on fish's health. From most of what I've read, .4 point ph changes (<48 hours) stresses fish, and can kill sensitive fish. I've experienced fish death from co2 related ph changes as well. It doesn't matter if the ph is co2 derived or someone dumped some hydrochloric acid into the tank.


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## geeks_15 (Dec 9, 2006)

> Originally Posted by geeks_15
> Its just that although pH is a measure of H+ concentration, so much can affect the pH besides just the H+ concentration
> 
> I am not sure of what you are saying. pH measures only the dissolved hydrogen ions (H+).


What I mean, is pH is affected by buffering capacity and the solutes in the water which can bind/release H+ and therefore alter the pH.

So pH = free H+ concentration. There is no doubt. I don't mean to question that. But pH (aka free H+ concentration) is just one of many components that make up healthy water.

Here is a bad analogy. Say you want to make a cake. The cake tastes good if you use x eggs and attain a certain fat content. But you don't have eggs. You can use lard to get the same fat concentration. You end up with the same fat concentration, but does the cake taste the same?

Maybe the H+ concentration in the water is the only solute in the water that matters, maybe it is not the only one but the main one, or maybe it is one of many that play a small part to make up healthy water for any certain species of fish. I don't know for sure.

But, I've never heard of someone using CO2 to set a certain pH for fish. A CO2 setup is fairly expensive and neons are historically (maybe not so much anymore) hardy, so maybe it is a good idea but was never needed in the past. I'm interested in apistos and I've read all I can get my hands on about them, and I've never heard of CO2 to control pH.


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## bartoli (May 8, 2006)

geeks_15 said:


> But pH (aka free H+ concentration) is just one of many components that make up healthy water.


Yes, I too believe that pH is one of the many factors contributing to healthy water for fish.

Since the level of pH (regardless of how it is achieved) affects health, why would you be surprised that lowering the water pH by CO2 can benefit neon tetra (a species of acidic water)?


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## geeks_15 (Dec 9, 2006)

I'm not surprised that it benefits them, I just wonder how much it benefits them. How do you measure benefit in a fish's health in an aquarium? And how do you narrow benefit down to one factor? Certainly neons don't need acidic water to live and act normally. I would guess that an acidic pH would be beneficial, but how do you know an unnatural CO2 level is not as much a negative as the acidic pH is a benefit?

I guess you could point to breeding as a sign of good health, but that is not an absolute correlation. I have harlequin rasboras in a tank that is cycling. I'm setting the tank up for apistos, so the water is soft with a low TDS. The water is stained with tannins from driftwood. I haven't tested for ammonia, nitrites, or nitrates so I don't know the exact water quality, but from my experience there should be some nitrites and maybe ammonia in the tank. The tank has been set up for 3 weeks. I just found some rasbora fry. So the water quality is probably less than ideal, but they bred. Did they breed because the water quality is better than I think or did the soft acidic water stimulate them to breed despite the suboptiaml water condition? The point is that I don't know. So changing one parameter might help. But just because you change one parameter and fish are healthy, it doesn't mean that your change is the cause.

Sometimes you can figure it out, but I think many fish keepers are guessing at the cause of problems and the cause of good health, me included.


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## geeks_15 (Dec 9, 2006)

BTW, I hope everyone is enjoying the discussion so far, I know I am. It is really making me think about how to set things up and how to improve things. I hope we can keep it going and get some more info on the topics we are covering. I think its been a good discussion so far.


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## bartoli (May 8, 2006)

geeks_15 said:


> How do you measure benefit in a fish's health in an aquarium?


I measure benefits in terms of the observed fish behavioral change. For example, how active are they? Are they playful? What is their appetite? Of course, also their death (I had observed a correlation between high pH and neon tetra death).



geeks_15 said:


> And how do you narrow benefit down to one factor?


By having the least interference to a tank. Don't muck around with a tank unless there is a good reason. With that approach, any major observed change is much easier to trace back to its cause.



geeks_15 said:


> Certainly neons don't need acidic water to live and act normally.


Certainly! But I enjoy seeing neon tetras being playful, not just surviving.



geeks_15 said:


> I would guess that an acidic pH would be beneficial, but how do you know an unnatural CO2 level is not as much a negative as the acidic pH is a benefit?


Behavioral observation tells me the net effect.


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## JeffyFunk (Apr 6, 2006)

geeks_15 said:


> Here is a bad analogy. Say you want to make a cake. The cake tastes good if you use x eggs and attain a certain fat content. But you don't have eggs. You can use lard to get the same fat concentration. You end up with the same fat concentration, but does the cake taste the same?


Yes, that's a bad analogy but not for the reasons you mention. Eggs contribute mainly protein to the cake batter, not fat. Fat in the cake batter is contributed mainly through ingredients like butter or oil or lard. For the topic of baking, I'd reference (almost) anything by Rose Levy Beranbaum. (Her Cake Bible I still consider the best primer on Cake Science.) Also good (scientific based) authors are Shirley O. Corriher and Harold McGee. (I'm not a fan of Alton Brown even if he also writes about the topic of food science). For more information on the topic of food substitutions in baking, I'd look up books on the topic of Vegan Baking.


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## geeks_15 (Dec 9, 2006)

Bartoli,

Let me start by saying that I agree with everything you said in your last post. I really think we are on the same page as far as the net effect and fish keeping as a hobby.

All of your answers are fine, but they are not objective and they are difficult to measure and reliably reproduce. They are fine for fish keeping. If it is working for you then that is great. Why change it? But they are not very scientific and they do not enable you to definitively identify the individual causes. I'm not saying I have the answers. I'm just saying scientific measurement and limiting the variables to one measurable thing is very difficult in the aquarium setting.



> By having the least interference to a tank. Don't muck around with a tank unless there is a good reason. With that approach, any major observed change is much easier to trace back to its cause.


I totally agree, but even if you leave it alone there are still many variables. Chemical reactions are happening in the substrate. The plants are growing and changing. Each water change adds new variables. The fish food content has all kinds of different substances. Bacteria and algae and other microorganisms are growing and dying off. Chemicals are left in the tank from your hands when you put them in the aquarium. The aquarium is a complicated biological soup that is hard to separate into single elements.

I'm sure adding CO2 sets off a whole cascade of events they we are unaware of. I believe the net effect is a positive for the fish in a planted tank. But I can't tell if it is the H+ concentration or something else. I'm not saying it isn't the H+ concentration. I'm just saying it is hard to prove that it is.

JeffyFunk,

Obviously I am no chef and I am humbled by your response.


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## bartoli (May 8, 2006)

geeks_15 said:


> All of your answers are fine, but they are not objective and they are difficult to measure and reliably reproduce. They are fine for fish keeping. If it is working for you then that is great. Why change it? But they are not very scientific and they do not enable you to definitively identify the individual causes. I'm not saying I have the answers. I'm just saying scientific measurement and limiting the variables to one measurable thing is very difficult in the aquarium setting.


Yes. And the more I read up on the scientific studies of fish physiology, the more I realize how little even the scientific community knows about the hard facts.

The life form that we know as fish is amazingly complicated. Like human, fish have feeling as well as fascinating cognitive capability. To people who are interested in the subject, I recommend the book:

"Behaviour and Physiology of Fish"

http://www.amazon.com/Behaviour-Physiology-Fish-24/dp/0123504481


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## Philosophos (Mar 1, 2009)

Wow, this thread took off when I wasn't looking.



geeks_15 said:


> It sounds like we are doing pretty much the same thing. I just use the pH monitor and you use the drop checker as a tool to measure the CO2 concentration. (BTW, the pH monitor doesn't have to be stationary. You can move it around the tank like you do your drop checker)


 Sort of; the drop checker will give more accurate CO2 readings since it's in a relatively closed system. Still, I wouldn't let it control my CO2 levels.



geeks_15 said:


> My tap water pH is 7.8 and I can get it down to 6.1 with CO2 pretty quickly (maybe an hour or two), so my tank is obviously different in that regard. I'm not sure what you mean by 25% fluctuation, maybe you could explain that statement in a different way so I can understand.


I just mean the basic understanding that .2 pH can easily change over a week without the CO2. This means your controller is working as if .2pH dropped because of CO2. That 25% is based on my experience of a drop to 6.3 from 7.1, and the .2 being 25% of that .8pH difference.



> I agree that just testing the pH won't tell you much. But using the pH monitor constantly and watching the changes that occur as the tank ages and you tweak different things, you can learn a lot and the pH monitor can give you good information. The main benefit of the pH monitor over a drop checker is that the pH monitor prevents rapid unchecked increases in CO2 that could harm the fish.


Drop checkers are much the same; they can be observed as things change in your tank, and you learn a bit more about flow dinamics. As you get more experienced with a drop checker, you find yourself using it less because of all the other indicators within the tank.

I agree that a pH monitor can be used to prevent rapid CO2 fluctuations if you set some major outlaying bounds. I'd want it hooked up more as an alarm system that shuts the CO2 off rather than deciding how to regulate it. At the same time, malfunction always spooks me with those sort of things; pH probes tend to drift at the end of their life.

The real bit that makes a pH meter kind of marginalized compared to a drop checker is that simply by dosing some NH4 and PO4 containing ferts, the pH will fluctuate and the readings will become more inaccurate. So long as you're working off a hobby titration KH test, you've got a resolution of 17.86ppm alkalinity presuming you've calibrated the kit. From there lets say you've got a decent pH probe; something accurate to .05pH. So if your tests say 4KH and 6.6pH in the tank using the pH-KH-CO2 method you've got 30.143ppm CO2 without consideration for other buffering systems. Now what happens with margin of error in your tests? If the water is actually 3.5KH and 6.65pH then you're sitting 23.507ppm, if it's 4.5KH and 6.55pH then you're at 38.048ppm. Now lets toss in even .1pH inaccuracy from other buffers; the accuracy decreases to a CO2 level that may be 18.672 to 42.691. This is the same as the maximum margin of error for a drop checker, and you can bet a tank will fluctuate by more than .1pH at any given time from other buffers.

As a solution I would propose even simply sticking the probe in a simple DIY drop checker,, or going a step farther and using the 4KH reference solution in an osmotic membrane that Tom and Vaughn have worked at. This would cut out a lot of interference; your KH would be dead accurate, and no other buffers would be interfering. After that the real question left is the reliability of the equipment, which would vary by brand and reliability of the maintenance.


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## geeks_15 (Dec 9, 2006)

Philosophos,

I think I understand the primary reason for our difference of opinion (regarding measuring and monitoring CO2 concentration in an aquarium). You demand more accuracy/precision from your equipment. I demand more convenience from my equipment.

I really don't care if the CO2 concentration is 18 or 42. I just want to have a steady CO2 concentration that is in the ballpark. The pH monitor allows me to set it and not quite forget it, but I can occasionally check it and be OK. The pH monitor gives me a safety feature since I don't want to have to worry about 18 vs. 42 and it won't let me get to 60 or 100.

So the next question is _should _I care about 18 vs 42 if I'm getting good results (good plant growth, algae in check, and good observed fish health)? Aside from the thought that having CO2 levels a little on the high side may be detrimental to fish health in the long term, that is.


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## geeks_15 (Dec 9, 2006)

BTW, I like your idea of making a DIY drop checker. I could easily make one with PVC and just use the pH probe. Good idea. I think I'll do it.


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## Philosophos (Mar 1, 2009)

18 vs 42ppm easily matters in my experience. I find at 18ppm-ish by drop checker is limiting and BBA creeps in quite quickly, but that I can identify the 30-48ppm range without fail. Just subjective observation, but you may want to try it for yourself to see if you notice.

The combo pH meter - 4KH solution thing is Tom Barr's I believe (that or he's just expanded on it greatly), applying it to a pH controller through CO2 addition is something birthed out of this thread I believe. Keep us posted on how it goes; maybe write a DIY if you find it works well.


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## geeks_15 (Dec 9, 2006)

> 18 vs 42ppm easily matters in my experience. I find at 18ppm-ish by drop checker is limiting and BBA creeps in quite quickly, but that I can identify the 30-48ppm range without fail. Just subjective observation, but you may want to try it for yourself to see if you notice.


I agree. I'm just not assigning a number to those observations. If plant growth is limited or BBA starts to develop, I just increase the CO2 going in. The pH monitor helps me slowly increase things and gives me a feedback mechanism.

That said, I'm going to start working on some sort of drop checker. I've made 2 this afternoon with the kH 5 and the blue water in the reservoir. This can help me put a number on the observations above and correlate the pH of the aquarium water (measured by pH probe) and the actual CO2 concentration (measured by the drop checker).

I'm afraid a drop checker with the pH probe may respond too slowly. I haven't given up on the idea, but I don't have the materials to make one right now anyway. I'll look around to see what Tom Barr has come up with.


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## Philosophos (Mar 1, 2009)

Ya, there's going to be a 2 hour average if you put the probe in the drop checker.

This post from VaughnH mentions tyvek for an osmosis based drop checker:
http://www.barrreport.com/showthread.php?t=2661

Here's his membrane based DIY drop checker:
http://www.barrreport.com/showthread.php?t=2585

And this would be Tom's thread working off Vaughn's idea, with both of them discussing its application for use with a pH meter:
http://www.barrreport.com/showthread.php?t=2456

Hope this helps your search some.


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## bartoli (May 8, 2006)

geeks_15 said:


> I'm afraid a drop checker with the pH probe may respond too slowly.


In my tank with pressurized CO2 I have a Red Sea drop checker filled with 4dKH solution. I noticed that the response time is very fast - in minutes, not hours. I suspect it is because the volume of solution in the drop checker is very small (note the drop checker's slopped design) and the amount of trapped air is tiny. By keeping those two factors in mind, a drop checker with pH probe may be workable.


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## geeks_15 (Dec 9, 2006)

I've ordered a Red Sea CO2 indicator and some pH calibration solution. This should allow me to correlate the aquarium pH with the CO2 concentration.

I made a couple DIY CO2 checkers, but I didn't like them.


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## geeks_15 (Dec 9, 2006)

I've had the red sea CO2 indicator for several days now. Here is what I have found.

The drop checker water is RO mixed to have a kH of 4.

At a pH of 6.5 (by my pH monitor) the drop checker solution is a yellow-green. At lower pH values the solution is definitely yellow. BTW my aquarium kH is about 4. I haven't let the CO2 concentration get any lower so far.

So the pH of my tank water is close to if not right in line with the values listed in pH/kH/CO2 concentration tables. Of course, tanks can change and tanks can acidify over time, though mine never have. But now with these two instruments combined I can determine the CO2 concentration in the water fairly precisely.

So what I've learned is to trust my pH monitor in regards to CO2 concentration. If the pH starts to change without changing the CO2 injection rate I can cross check the CO2 concentration with the drop checker.

Also, I had been wondering if my sump setup (see me journal linked below for details) was causing too much water surface disturbance and I was losing too much CO2, but that is not the case. I can readily exceed the recommended CO2 ppm for fish and maintain that level.

I had been running too much CO2 with values definitely exceeding 30-40ppm. Interestingly the only ill effect demonstrated by the fish was the eggs of my nannacara anomala not hatching over several spawnings. No fish have died and their behavior has been no different than normal as far as I can tell.


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## jestep (Nov 14, 2009)

Keep an eye on the fish for sure. Too much CO2 can have 2 effects. Short term would be asphyxiation if the O2 level gets too low. Generally CO2 doesn't displace O2, because the water can absorb much more gas than what you can reasonably supply. The other would be CO2 poisoning, which can occur over a longer period of time. CO2 poisoning causes everything from asphyxiation to kidney failure. I would strongly suggest keeping the CO2 below 30ppm. You're fine now, but you may be causing irreparable damage to your fishes organs.


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## rjfurbank (Jan 21, 2008)

Great thread! Thanks everyone for the intelligent discussion. I'll add a few comments and try to keep it going. . .

I have had nearly continual BBA issues in my 90g tank (kept in check through rigorous use of XL). I keep returning to the CO2 setup as that seems to be what everyone recommends to get rid of BBA.

I use a CO2 reactor (aquamedic 1000) plumbed into an Eheim 2217 outlet. I do not use a controller--just adjust bubble rate to keep drop checker light green/yellow (4 dkH DI water). I have tried both things including timing CO2 w/ lights; running 24/7. The only difference between the two was that my CO2 ran out much sooner.

I have recently noticed that my drop checker takes some time to reach "steady state" after lights (and CO2) on. CO2 also accumulates in the reactor over the photperiod. Based on this I have added my CO2 to it's own timer and have started turning it on 1hr before lights on and turning it off 30 minutes before lights off to let the accumulated CO2 dissolve.

*So--my question is: does anyone have experience with this?* My goal is to get the CO2 stable and set at the optimum level when the lights turn on and not to waste alot when the lights are off.

Thanks,

-Roy


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## geeks_15 (Dec 9, 2006)

I have done the type of CO2 timing you describe. I think having the CO2 on a separate timer is a good idea if you choose not to have it on 24/7. It will take some time to get the CO2 levels up to the desired level after being off overnight. I say some time because I think the time it takes will be variable depending on amount of gas off overnight, CO2 setup including diffuser efficiency and bubble rate, size of the tank, etc. I would just watch it and adjust the timing as needed. Some people say it takes 2 hours to get their CO2 levels up to their desired level. Others say 30 minutes.


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## Philosophos (Mar 1, 2009)

Geek15, I'm happy to hear you've got a column that applies to the kh-ph-co2 method. But at the same time, I wouldn't trust that current stability. One ammonia spike throws things off completely; KH will register the same while pH will increase. Having a pH monitor around is nice, don't get me wrong, but water chemistry is a dynamic system that pH alone will not measure accurately in regards to CO2. This is why automatic CO2 adjustment remains inaccurate.

30-40ppm CO2 is about where I keep my tanks. What people call, "too much" on these forums gets updated regularly without much of a basis; it used to be considered 15ppm. My own experience leads me to believe 60ppm is about the highest I'd push it for shrimp, though more like 75ppm for fish. There's really no good research I've been able to find on CO2 LC50's as it relates to the hobby. The Ecotox database showed up some low LC50's around 10-30something ppm for atlantic salmon, but that's about it.

rjfurbank, check this post out for a pH monitor's readings of monstrous planted tank; 1500 gal or so. It looks like about 1:15 to get CO2 to non-limiting levels in this tank. The number I'm hearing more frequently for smaller tanks is about a half hour. All of this will vary depending on your injection method; regular diffusers aren't so great, reactors are a bit sluggish at times. I've found needle wheels establish very quickly.


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## rjfurbank (Jan 21, 2008)

Thanks guys--I have been looking into needle wheels as well but really don't want to add another piece of equipment if I don't have too. . .

My reactor is very sluggish. I plan to slowly move the time it kicks on before the lights on such that the drop checker is a very light green color at the beginning of the photoperiod (and fish are not stressed). Today was the first day and it was set to 1 hr before the lights. Drop checker still pretty green so will likely move the time--will watch it for a few days though before tweaking further.

Dan--thanks for the link--always love seeing the data. . .

-Roy


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## Philosophos (Mar 1, 2009)

Drop checkers can take a good while to react; 2 hours is the popular estimate. I find mine takes about 1-1.5 hrs filled half way up. Why drop checker are round is beyond me; you get faster reactions with a high surface area to volume ratio.


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