# [Wet Thumb Forum]-Questioning recommended CO2 levels



## DaveStall (Feb 14, 2003)

This is something that I have always wondered about when I see "recommended" CO2 levels. Isn't it true that we are talking about excess CO2 in the water? If I take a pH and KH reading and determine that I have 20ppm CO2, that means I have 20ppm of CO2 in the water that isn't being utilized doesn't it? What got me thinking about this topic is my 75g aquarium. My KH is 1, my pH is 7.4 and I have one yeast type CO2 generator on the tank. If I take the generator off, my pH still stays at 7.4 or so, but the plant growth slows down quite a bit. What this tells me is that the plants are utilizing all of the CO2 I am adding to the water, and that CO2 is beneficial to the plants. It also probably tells me that I should be adding more CO2. However, I don't see the point of adding so much CO2 that I am reading an excess of anywhere close to 20ppm (or whatever the "recommended" level is). It seems to me that any reading that points to an excess in the water would tell me that I am adding more than enough CO2 for the plants.

I would be interested in hearing other's thoughts on this as well.

Dave


----------



## DaveStall (Feb 14, 2003)

This is something that I have always wondered about when I see "recommended" CO2 levels. Isn't it true that we are talking about excess CO2 in the water? If I take a pH and KH reading and determine that I have 20ppm CO2, that means I have 20ppm of CO2 in the water that isn't being utilized doesn't it? What got me thinking about this topic is my 75g aquarium. My KH is 1, my pH is 7.4 and I have one yeast type CO2 generator on the tank. If I take the generator off, my pH still stays at 7.4 or so, but the plant growth slows down quite a bit. What this tells me is that the plants are utilizing all of the CO2 I am adding to the water, and that CO2 is beneficial to the plants. It also probably tells me that I should be adding more CO2. However, I don't see the point of adding so much CO2 that I am reading an excess of anywhere close to 20ppm (or whatever the "recommended" level is). It seems to me that any reading that points to an excess in the water would tell me that I am adding more than enough CO2 for the plants.

I would be interested in hearing other's thoughts on this as well.

Dave


----------



## Roger Miller (Jun 19, 2004)

How is the algae in that tank?

I think I'm with you. I don't and have never tried to keep anything like 20 ppm of CO2. In my experience, some CO2 is usually enough and levels of 5-10 ppm are plenty.


Roger Miller


----------



## DaveStall (Feb 14, 2003)

The algae (or actually cyanobacteria) in that tank is bad, which I'm sure is another indication that my CO2 levels are too low. I'm not saying I am doing CO2 correctly in that tank, it's just that I often see people recommending fairly high CO2 levels and I just recently started to wonder why.

Dave


----------



## Mortadelo (Mar 14, 2004)

Hi,

You may find this article interesting Dave http://www.tropica.com/article.asp?type=aquaristic&id=142

I am the High CO2 type of aquarist. Never succeded in growing plants without supplemental CO2, perhaps because my tap water is hard and alkaline. Others with soft and acidic water may enjoy naturally higher CO2 levels, just add a moderate fish load and you will have a fair amount of dissolved CO2, that does not happend in hard water.

I think we should realize each plant has its own CO2 requirements, I do not think Rotala macrandra and Ceratophyllum demersum have the same requirements for CO2, C. demersum can even use bicarbonates.

I use high CO2 (20-30 ppm) in both very high and very low light tanks.

In low light tanks CO2 injection can compensate for poor lighting (see article above). See my 250 gallon here to see a low light / high CO2 tank. http://aquabotanicwetthumb.infopop.cc/groupee/forums?a=tpc&s=4006090712&f=5196060812&m=1316029563

Saludos.

My planted aquarium blog
http://www22.brinkster.com/aguaverde/articulos/diario.htm


----------



## Vicki (Jan 31, 2003)

Well, there are many ways to success in this hobby. My water is on the high end of moderately hard (GH 11-13, depending on the time of year), and slightly alkaline; I have three tanks with moderate light to which I add no CO2 at all, and get good plant growth (primarily low light plants-crypts, java fern, java moss, anubias, with some watersprite thrown in), and no algae problems. Years ago George Booth recommended 15 ppm, and that's pretty much what I've always stuck with in my tanks that have CO2 injected. I've tried higher levels of around 20 ppm, but really saw no significant difference. My rotala macranda does very well at that level (i.e., at 15 ppm) as long as all its other needs are being met.

http://www.wheelpost.com


----------



## DaveStall (Feb 14, 2003)

I agree with both of you that there are any number of ways to achieve success in this hobby, and I would never suggest anyone is doing anything wrong. However ... lol

If you are running your tanks at 15 or 20 ppm CO2, I am assuming that you are determining that level by reading the pH/KH/CO2 chart. If that is true, that means you are actually running your tank at 15 or 20 ppm _excess_ if I am looking at this correctly (which I may not). If that is true, doesn't it mean that you are actually supplying 15/20 ppm of extra CO2 that isn't being utilized by the plants?

I can see supplying extra CO2 if you are needing a particular pH level in the tank, but not for plant growth. Anyhow, I'm not trying to criticize anyone, I am just trying to grasp what it really means when we measure the CO2 level in the tank. Part of what has got me wondering about this is my above mentioned 75g tank. I took my CO2 off when fighting my bga problems, and I left it off because by my measurements I had hardly any CO2 in my tank at all. When I did that, my rotala macrandra (which accounts for probably 60% of the plant mass in that tank) just stopped growing completely. When I added the CO2 back, my readings stayed the same for pH, but the rotala exploded back into action. What that seems to tell me is that I am getting CO2 in the water, but it is all being utilized and thus looking at the KH/pH/CO2 table isn't actually telling me how much CO2 I am adding to the water, it only tells me how much CO2 is in excess. I would think if I could add enough CO2 to lower the pH by even .1, that would tell me I am adding enough to the tank because I am now adding CO2 in excess. If that CO2 is in excess, that means nothing is utilizing it and thus it seems pointless to me to add any more.

Dave


----------



## Vicki (Jan 31, 2003)

LOL! Stop, you're making my head hurt! First of all, I rely a lot more on how my plants look than I do on any actual numbers; it just so happens that the point at which they are growing well, pearling and at which I have minimal visible algae is right around 15 ppm, which I determine by measuring the ph and kh. How close that is to the actual CO2 concentration I have no idea, there are too many unknown factors that could affect the number we read on the chart, but I know that my plants are happy at that number, so I stick with it. My attitude toward plants is probably a little different from many of the other people who post here. I love my plants, but I will do nothing for my plants that will in any way compromise the well being of my fish, they come first, and I am very conservative when it comes to adding ANYTHING to my tank. I much prefer to add back phosphate with water changes (my tap water varies between about 1 and 1.5 ppm), but that necessitates two big changes a week to my 120 gallon, and I just don't always have time, so I do add SeaChem Phosphorous when I just can't manage an extra water change. I also have a rule that I make most of my plants adhere to: PERFORM OR DIE. If it won't grow for me and look beautiful, I'll grow something else. I don't have time to fiddle endlessly just to make one plant happy, and there are too many other beautiful plants out there. Of course, there are always exceptions-some plant that I'm determined to have or can't bear to part with-but for the most part, if the plant don't grow then out it go.

http://www.wheelpost.com


----------



## skunky (Jun 22, 2003)

Good post Vicki. I agree, I too like my plants, but I am a fish keeper not an aquatic gardener and they come first. I only grow plants mainly for my fish, nothing to extravagant, they appear to enjoy them, so I'm happy. Each to their own!

I have on a few occasions found myself trying to match my water to the plants and not the fish. If they grow, great, if they don't.....tough. As long as my fish are healthy!

'Nothing is that easy'


----------



## Anthon (Feb 26, 2004)

I think (I'm not sure) that quite high levels of CO2 must have a positive effect on CO2 diffusion around the leaves (diffusion is link to concentrations gradients).

_____________________________
Sorry for my bad english ...


----------



## countrymouse (Jul 6, 2003)

This is really interesting, especially in light of the number of experts that have told me that I can't possibly get enough CO2 into my 55g with DIY yeast method. (Incidentally, the CO2 has dropped my pH from 7.4 to 6.8, which is a bit much.) I think it makes sense that the steady carbonic acid levels represent what's not being taken up. 

Before I got the big juice bottle and started feeding the tubing into my H.O.T. Magnum, my plant growth and color had already improved with the two Hagen systems on the tank, even though I didn't get a noticeably different pH reading. It probably had made a very small but unreadable difference. Even so, the seemingly excessive amount I have now (according to the kH/pH calculator) isn't stressing my fish. Even the big swing back up to the original pH a couple of days ago (when the tubing came out of the generator lid) didn't stress them. 

But I agree with Vicki about the fishes' needs coming first. It's the fish that got me into this hobby in the first place.


----------



## DaveStall (Feb 14, 2003)

I was pretty much told the same thing about using yeast bomb CO2 on my 75g tank. I can saw that from what I have seen, any addition CO2 you can add to the tank is better than none. My plants grow measureably faster with a yeast bottle running than without. That being said, I also have to agree that I am most likely not adding enough CO2 as the plants seem to be utilizing all that I am adding which means they probably want more. It is interesting that your pH showed such a significant drop from using a single bottle, as I wouldn't have expected that. Would you mind positing your KH reading just to satisfy my curiosity?

I'll put a "third" on Vicki's comments as well. The main reason I have not added a pressurized CO2 system is that I am worried about killing fish while I am trying to get the CO2 levels set correctly. I have a very low KH (around 1), and the thought of adding buffers (pH goes up) followed by CO2 (pH goes back down) worries me a bit.

Dave


----------



## countrymouse (Jul 6, 2003)

My kh is between 6 and 7 degrees, and it's not entirely clear whether my base pH is 7.4 or 7.6 based on the test I use (Aquarium Pharm). Anyway, I have decided to back off on the CO2 (by using less of everything) and also reduce my kh over the next few weeks (with water changes) to about 4 degrees. That should still be high enough to avoid a pH crash, and I'm going to aim for 10ppm on the CO2. Should be enough, I think. I have to add some buffering because my tap water kh is 0.


----------



## Jim Miller (Feb 3, 2003)

i wonder if the concentration of "excess" co2 helps drive a reaction in the plant. i seem to remember that some reactions are concentration sensitive.

jtm (college chemistry last studied in '66...)

Tank specs in profile


----------



## Vicki (Jan 31, 2003)

You can certainly add enough CO2 with a DIY setup to make a difference, even in a larger tank. The big problem there is that it is so difficult to maintain a constant supply. Fluctuations in your CO2 supply can cause algae problems, and are going to bounce your ph around some too. Jim, pressurized CO2 is actually safer than DIY because you can control the supply so much better. Setting it up and adjusting it shouldn't cause any problems for your fish at all, as long as you take things slowly and test frequently. As long as you have a good needle valve, once you get it set where you want it you should never have to change it (although of course it's a good idea to monitor your ph and kh regularly). And raising your KH doesn't need to be problematic either if you do that the same way--slowly, and test your ph frequently. Baking soda does a nice job of raising the KH, and can be added in increments that won't cause a significant increase in ph. If you don't add more than 1/4 teaspoon per 20 gallons at a time, you won't see a big ph jump. And the stability you'll gain by raising the KH makes it worthwhile.

LOL! It's just occurred to me that 1966 was the last time I had a college chemistry class, too!

http://www.wheelpost.com


----------



## Roger Miller (Jun 19, 2004)

Regarding the safey of DIY CO2 compared to pressurized. Probably as many fish have died from accidents with yeast CO2 as have died with pressurized CO2. I have a lot more confidence in the saftey of my pressurized system than I do in the safety of my DIY yeast setups.


Roger Miller


----------



## Vicki (Jan 31, 2003)

> quote:
> 
> I have a lot more confidence in the saftey of my pressurized system than I do in the safety of my DIY yeast setups.


Yes, so do I. I'm down to one tank where I use DIY CO2; I just got a nice little powered reactor for it, and I'm afraid to use it. At present, my CO2 line goes directly into my AquaClear, and is already putting 15-20 ppm into the tank, and I'm afraid the powered reactor will result in TOO much CO2 in this small tank. This is my plant nursery, a 20 high where I put new plants and plants I'm trying to encourage along, but it's also home to my Corydoras sterbai and ottos, and two SAEs I borrowed from a larger tank to clean up a BBA and staghorn outbreak that resulted from the CO2 fluctuation I talked about in my previous post. I'm setting up a 30 gallon high light tank next to it and just got a new CO2 system for that one, and I'm going to get a manifold so I can run both tanks off that bottle. Until I have pressurized CO2 on that tank, the powered reactor is on hold. This is the only tank in which I DO have occasional algae problems, and I have no doubt that it's the inherently uneven CO2 supply that causes that. And I freely admit it's almost always my fault--I get busy and I don't change the bottle as often as I should.

I wanted to make one thing clear about what I said above. I didn't in any way mean to suggest that people who started with plants or concentrate on their plants above everything don't care about their fish. It's just that you need to do things a little differently if the fish happen to have been there first; you have species to deal with that you might not have chosen if you had set up the tank for plants from the beginning. The fact is that plants are a wonderful addition to ANY tank, and they do wonders for the fish; healthy, growing plants contribute to their well-being in a way nothing else can (except water changes!). If you start with the plants, you have the luxury of selecting species that will be comfortable in the kinds of conditions you will create to favor the plants' growth. All I meant to suggest is that before I add anything to my tanks, I want to be very sure I'm not compromising my fishes' well-being in any way and that I'm still going to have a stable, healthy environment for them AND the plants. That's part of the reason I prefer to add as little CO2 (or other nutrients) as possible to achieve the results I want with my plants.

http://www.wheelpost.com


----------



## Jim Miller (Feb 3, 2003)

never questioned the safety or efficacy of pressurized over diy. i did the diy thing on my little tank back in sacto last year and now will only do pressurized, or if tiny just nothing or excel.

have fun

jtm

Tank specs in profile


----------



## countrymouse (Jul 6, 2003)

Stability question:

While I haven't seen any signs of stress yet, I want to make the environment as stable for both the plants and the fish as possible (but without going pressurized: I just recently added the extra lighting and to keep peace in the house I'll have to wait a long time before asking for anything else expensive). If I run two yeast bottles at a time connected to a gang valve, and changing them at different times, shouldn't that keep the pH more stable? In addition, as I posted previously, lowering the buffering capacity a little and the ppm of the CO2.


----------



## Vicki (Jan 31, 2003)

> quote:
> 
> never questioned the safety or efficacy of pressurized over diy.


No, you didn't--sorry! I meant to direct my comments to Dave Stall, Jim.

Countrymouse, I'm not sure why you want to lower your KH; it's fine right where it is. If you want to keep your ph stable you don't want to reduce the buffering capacity of your water. Your plan to run two bottles and change them at intervals should help a lot. I change my bottle weekly, but I'm only running DIY on one 20 gallon tank. As long as you change them before the CO2 output drops significantly, you should be okay.

http://www.wheelpost.com


----------



## countrymouse (Jul 6, 2003)

Thanks Vicki, maybe I'll keep it where it is, then. Is 6.8 ok for a pH target with the kh I've got? (between 6 and 7).


----------



## Jim Miller (Feb 3, 2003)

vicki

no offense taken! i assumed you were really replying to dave.

have fun!

jtm (in new house in parkton, md, and hankerin' for a tank...)



> quote:
> 
> Originally posted by Vicki:
> 
> ...


----------



## Jack11 (Mar 30, 2004)

OK,
I don't mean to stir all this up again with what is, most likely an incredibly stupid question but, if you raise the kH of your water, does this allow you to put a greater concentration of CO2 into the water? Based on the CO2 tables I have seen, it seems that the greater the kH the greater the CO2 concentration for the same pH. For example according to URL=http://www.tropica.com/default.asp]Tropica's table[/URL], with a pH of 7.0 and kH of 6, I have a CO2 concentration of 19. This is not bad for a planted tank, however, if I raise my KH level to 12 with carbonate buffers of whatever kind, I have a CO2 concentration of 39 which might be dangerous for some fish. So, if I added CO2 at the same rate, would I have a greater concentration in my water if I were to raise my KH? Not that I'd ever want to raise my KH that high, just asking to try and better understand this equation. Thanks
Jack

Ah Hah! You're supposed to put the plants IN the water...


----------



## Vicki (Jan 31, 2003)

No, not if you don't change the amount of CO2 you're injecting. If your ph remained the same, the CO2 concentration WOULD be higher-but what will happen is that your ph will rise as you increase your KH, and the CO2 level will stay the same. In order to increase the CO2 concentration you would have to inject additional CO2, which would then reduce the ph from the level to which the baking soda had raised it, but the KH level would remain the same-consequently, you would have a greater CO2 concentration.

http://www.wheelpost.com


----------



## Jack11 (Mar 30, 2004)

Makes sense. Thanks for clearing that up. Brain's a little foggy this Monday morning, I guess!

Ah Hah! You're supposed to put the plants IN the water...


----------



## Jon Mulzer (Mar 9, 2003)

Countrymouse, instead of the gang valve I would suggest using a solid plastic airline "T" if you can find them. I tried the gang valve thing once and found that it leaked. And since my CO2 line was terminating in a pressurized area I found a nice puddle of water on the carpet. At the time I was using the "T" when it would come time to change bottles I would just double the hose over a couple of times to kink it off (once isn't enough, it will still leak) and then wrapped a rubber band around it to hold it.

Vicki, the "PERFORM OR DIE" comment got a good chuckle out of me. That is my philosophy also. If it doesn't grow for me, oh well. There is bound ot be something else out there that can take its place. And trust me, I needed the chuckle after how things have been going lately, lol.

----------------------------

15XH, 36W PC, XP-1, Onyx Sand, DIY CO2

Crypts spiralis, ciliata and wendtii bronze and red, pennywort, wisteria and java fern and moss.


----------



## gsmollin (Feb 3, 2003)

> quote:
> 
> Originally posted by DaveStall:
> This is something that I have always wondered about when I see "recommended" CO2 levels. Isn't it true that we are talking about excess CO2 in the water? If I take a pH and KH reading and determine that I have 20ppm CO2, that means I have 20ppm of CO2 in the water that isn't being utilized doesn't it? ...
> ...


The equilibrium level of CO2 in the water is 3-5 ppm. Anything beyond this level is indeed, "excess". You won't find it in nature.

There are also other things in your aquarium that you won't find in nature- namely the aquarium! Plants grow in the wild under rather different conditions than exist in your aquarium, and in any kind of "Dutch" aquarium, the juxtaposition of plants is never found in nature. So this is a highly artificial situation. It may call for artificially high CO2 levels.

For instance, my tap water is KH=4, but unless I keep the CO2 levels at 20-30 ppm, the KH falls rapidly because the plants are absorbing carbonate from the water. In nature, there is always more water available, but in my dinky aquarium, there is only ~40 gallons.

So the ultimate answer is that the "recommended" levels are recommended because they make the plants grow well, and mitigate many of the other shortcomings of an aquarium. There is no attempt at hedgemony. Any CO2 you supplement is better than none, and you are likely to see improvement. However, demanding plants usually require 20-30 ppm CO2 concentration, and high light, and supplemental fertilizers, and supplemental trace elements, and on and on and on, to grow in an aquarium.


----------



## countrymouse (Jul 6, 2003)

Thanks, Jon

I already don't like the gang valve I bought yesterday; too stiff to adjust easily. I do use a check valve, though, so I don't think there will be puddles. 

Thank you to gsmollin, too, for explaining why the CO2 concentration needs to be high (compared to nature). That makes sense.


----------



## DaveStall (Feb 14, 2003)

Sorry .. double (triple) post


----------



## DaveStall (Feb 14, 2003)

> quote:
> 
> Originally posted by DaveStall:
> 
> ...


----------



## DaveStall (Feb 14, 2003)

Sorry again .. seems like whenever I try to edit a post with a quote I get a new post instead. Please forgive the numerous typos in the above post.









Dave


----------



## Anthon (Feb 26, 2004)

High CO2 level have effect on diffusion speed of CO2 (according too Fick Law).

Near the leaves of a plant CO2 level is lower than tank CO2 level because CO2 is "eaten" by leaves during photosyntetis. So CO2 have to diffuse from free tank water (with high CO2 level) to leaves. Gas diffusion in water is quite slow. But the higher the concentration difference is between free water and the leaves is, the faster the CO2 will diffuse and will be available for the plant.

With slow level such as 5 ppm and high photosyntetic activity you can have free CO2 in your tank but nearly no free CO2 available for plant (plant can absorbs CO2 faster than it can come to its leaves).

I hope my explication is clear enough.

_____________________________
Sorry for my bad english ...


----------



## DaveStall (Feb 14, 2003)

Thank you Anthony!

I knew somehow the higher CO2 levels _were_ most likely beneficial, but I just couldn't wrap my mind around it. Your answer does clear things up quite a bit. I knew I shouldn't have skipped all of those chemistry classes ...

Dave


----------

