# CO2 levels and KH



## LAKA (Feb 11, 2007)

I have a 180 gallon heavily planted tank that i have just introduced pressurised CO2 into at 2.5 bps.
I have a standardised 4 degree ref. sln. in a drop checker. I have mild surface agitation using a powerhead 24/7 . The CO2 is linked to lights via solenoid.
I am aiming for 30ppm CO2. Solution is still blue. I do not want to reduce surface movement any further as i fear my angelfish will start gasping at the surface. Only other option is to raise CO2 rate.

My question is will a higher KH let me reach my desired CO2 level quicker than a low KH.
Put another way assume we have 2 identical plants in every way except for KH. One tank is KH1 the second tank KH 10. Same water chemistry otherwise, same number/type of plants same substrate same fish population same rate of CO2 input same everything else. Which tank will have higher CO2 dissolved in it at the end of the day?

LAKA


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## eklikewhoa (Jul 24, 2006)

I would think the 1dKH would have more co2 if I'm not mistaken....lower kh allows for better co2 in the water column.


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## LAKA (Feb 11, 2007)

That does not make sense to me. The ph/KH/CO2 table shows for a given pH the higher the KH the higher the CO2 levels. I know the pH should be read as the end result. I am not overly concerned about pH levels in my tank, but would like to know how KH affects dissolved CO2 levels in a CO2 injected tank.
LAKA


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## eklikewhoa (Jul 24, 2006)

if the kh is high and the ph is low then the co2 had to do a lot of work to bring down the ph to overcome the Kh which would give you the high co2 reading.


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## Edward (May 25, 2004)

LAKA said:


> My question is will a higher KH let me reach my desired CO2 level quicker than a low KH.


 I don't think there is going to be a difference. Look at CO2 as it was an acid in gas form dissolving in the water column. Acid moves pH down and alkalinity KH moves pH up.


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## vicpinto (Mar 27, 2007)

LAKA said:


> ...same rate of CO2 input same everything else. Which tank will have higher CO2 dissolved in it at the end of the day?
> 
> LAKA


You just answered your own question. If you have the same rate of CO2 input them you must have the same amount of CO2 dissolved. You cannot have "the same water parameters" for a KH of 1 and a KH of 10 because as soon as you raise the KH the pH goes up too to maintain a constant amount of dissolved CO2.

Example:

KH1, pH6 for 30ppm (assuming any pH - I chose 6 and assuming your "constant source of CO2" results in 30ppm)

versus

KH10, pH7 for 30ppm (CO2 needs to be constant per your scenario (30ppm) and KH is now 10 per your scenario. Looking at the chart, pH *HAS* to have risen to 7. This is in conflict with you scenario of having the same water parameters - you cannot.

Obviously, if you are using any type of pH buffer then the chart is useless. The chart assumes that CO2 is the only thing that controls the pH.

People make the mistake of just reading down the KH line of the chart and saying: "If I have 30ppm of CO2 with KH1 of 1 then I will have 300ppm of C02 with a KH of 10". That is incorrect. You cannot have more of something if you haven't increase the rate at which it is been added.


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## LilLou (Apr 23, 2006)

Correct me if I am wrong but my understanding of it was that KH acts as a buffer to the acid by binding with it preventing it from causing a pH drop.

So when we add the CO2 into our water and it magically turns into carbonic acid in the water (can you tell I hated Chemistry) We know the CO2 is in the water because of the pH drop.

The water with 1 KH has a smaller buffring capacity than water with a KH 0f 10. 
So in my head it would take more CO2 to achieve a concentration of 30 ppm due to the fact that some of the KH will bind the acid to keep the pH stable.
If the above holds true then it would take less CO2 for a tank with 1KH. 

If the CO2 is bound is it readily available for the plants to consume??
If this is true and the CO2 is available even when bound then they both use the same amount of CO2.

I am leaning towards option #1

At the end of the day most likely both will show a ppm of 30 but it will take more CO2 in the tank with the higher kH to get there.


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## MrSanders (Mar 5, 2006)

Given that you are using an efficent way of dissloving the CO2 gas into your water... there is only one way in which to get a high concentration of CO2 dissloved. That is to Add more CO2.... There is no magic way to add or take away KH to allow you to have more dissloved gas. Its pretty simple, if you want more CO2, you need to add it at a higher rate


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## Edward (May 25, 2004)

LilLou said:


> At the end of the day most likely both will show a ppm of 30 but it will take more CO2 in the tank with the higher kH to get there.


LilLou,
I don't think you get it right. 

Water without carbonic acid (zero CO2) has a pH of 8.3. Water with maximum dissolved carbonic acid (max CO2) has a pH of 5.65. 

Water without KH (no baking soda) has a pH of 5.65. Water with maximum KH (max baking soda) has a pH of 8.3.

Now by mixing these two (CO2 and KH) the pH will go to a value expressed in table below:










Edward


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## dennis (Mar 1, 2004)

Think about adding an amount of CO2. We measure it in ppm because that is the conventional way, but that ppm ( or mg/l) is simply a measure of the ratio of CO2 to water. My injecting 2 bubbles per second, you are adding some volume of CO2 gas into some volume of water. KH does not affect how much is added. kH _only_ regulates how much CO2 is converted into carbonic acid, which we see indicated by pH. kH is like a sponge, more kH equals a larger sponge which means more CO2 is absorbed before you notice a change in pH. The kH/pH charts can be confusing because you notice the change is not linear. This is not actually because of the kH but because of the mathematical way pH is measured. Because pH is calculated as a negative logarithm of the concentration of acid, large changes in concentration show up as a gradual change in pH... but you hated chemistry so ignore the words math and log

LAKA, so, to answer your question- changing your kH will not affect the amount of CO2 in the water. The only way to change the CO2 in the water is to add more. Lets say that at kH 1 adding Co2 at 3bps gave you "30ppm". If you change the kH to 5 (or 50 for that matter) but keep the rate at 3bps, you'll still have 30ppm in the water.

To answer you question more, I have found that for every 100liter aquariums, 1 bps is a good starting place for adding CO2. You may have to tweak a little up if you have a bubble counter that makes smaller bubbles than mine or down if you have less aggitation, or if plant growth indicates it, but that is a good starting place. Since you have a large tank (~675 liters) then I suggest you start with a bubble rate of 4 per second and increase if the plants seem to require it. Keep an eye on the drop checker while you do this and see if you observe any change.


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## BryceM (Nov 6, 2005)

I have a 180g tank with about 3.3 wpg MH/T-5 lighting and a DIY CO2 reactor made from 3" PVC pipe. I keep the water at a KH of around 2 or 3. There is some, but not much surface disturbance. pH is controlled between 5.95 and 6.15 by a Pinpoint controller. The CO2 stream in the bubble counter is much too fast to count. It runs about 10 hrs/day intermittently but it doesn't cycle on or off all that often. A 20 pound cylinder lasts about 6 months.

As the others have eloquently stated, the KH level has no bearing on the concentration of dissolved CO2. At a low KH it will require a lower pH to acheive 30 ppm. At a higher KH you will achieve 30ppm CO2 at a higher pH. CO2 in the water is a little like having a bank account. If you didn't put something in the account, it isn't there, no matter what any test or gadget tells you. Most of the time, watching the bubble count is the best way to gague how much is going in. In a 180g the aquarium is so big that the rate is hard to judge in a standard bubble counter.


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## dennis (Mar 1, 2004)

guaiac_boy said:


> Most of the time, watching the bubble count is the best way to gague how much is going in. In a 180g the aquarium is so big that the rate is hard to judge in a standard bubble counter.


Fun, but probably pointless, DIY project material there. Lets see, 6" CPVC, modify the bottom 1" slip to 6 slip coupler so the 1" passes through into the counter chamber..... you may have to put a trap at the bottom so the gas build sup into one big bubble.......

Its late, sorry


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## LilLou (Apr 23, 2006)

Dennis,

If the higher KH equates to a bigger sponge, then it absorbs more CO2. That being said is the CO2 thats in the bigger sponge available to the plants?

When I first started doing this I was told not to use the chart because it was misleading. My water right now at home is 5.5 pH with a KH of 1. So with no CO2 being fed into the tank my CO2 level should already be where according to the chart?

Now if I take my tank water and let it gas out for a day take that pH and drop it by 1 with CO2 will I arrive at 30ppm or close to it?? That's the way I have done it in the past always had good pearling and fish never at the surface gasping. Is there something wrong with that method now?

Not trying to be argumentative just trying to make sense of all this chemistry. Did I mention I hated chemistry in high school?


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## LAKA (Feb 11, 2007)

Thanks for the fantastic responses guys.
General consensus is KH affects end result of pH but 30ppm CO2 is 30ppm CO2.
Guaiac boy reading your tank description is like describing my tank exactly Same CO2 cylinder size, wattage, light types. I have 3-4bps? can't count well at this rate. I noted only my angelfish started gasping when i cranked up CO2 . Neon tetras and siamese flying fox/red tail shark/otos/bristlenose all behaving normally.
Does anyone else have angelfish? Are they more sensitive to high CO2 levels ie. those approaching 30ppm?


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## dennis (Mar 1, 2004)

LilLou, in short, yes. The CO2 that is dissolved is available in two ways, as carbonic acid (HCO3-) and as microbubbles of gas. Any pH drop you experience is the result of carbonic acid, more or less. When CO2 dissolves in water, two steps or processes occur after the initial dissolving:

Initial step: CO2 + H2O <=> H2CO3 (carbonic acid)
step 1: H2CO3 + H2O <=> HCO3-(bicarbonate) + H3O+
step 2: HCO3- + H2O <=> CO3^2-(carbonate) + H3O+

In both steps the formation of H3O is your actual acidity as pH is measured as -log[H3O].

Other things can affect acidity and that is the reason your pH is 5.5 with kH of 1. Something else is adding to that acidity. I would personally raise the kH to 4-5 so that the addition of CO2 does not create such and acidic environment. If you currently have a method that works though, stick with it, IMO. If you feel this is not working though, I really suggest you increase the hardness of your water and then use a drop checker with 4dkH as your CO2 indicator. The increase of the aquarium kH is only to prevent your water from becoming extreemly acidic with the addition of CO2 and not because the kH affects the amount of CO2 you need or have available.

Also, FYI to all: if you look at step 1 above, you can see why adding Na or KHCO3 (baking soda) to your water will increase the pH. If you add a form of HCO3 to the equation, it is out of balance on the right side and the equation will be pushed to the left. H3O is converted to H2CO3 and acidity is removed. It is important to realize (most don't) that having carbonic acid, or any acid, does not yield a lower pH. It is the conversion of the acid to a free H+ ion that makes the acidity not the actual presence of the acid. So, adding bicarbonate to your aquarium does two things; it prevents the acid from releasing its H+ and actually converts free H+ into the acid, where it cannot escape. This increases the pH overall. This may also be why (speculation on my part) why some plants do not do well at higher kH as the additional buffering prevents the plants from having easy access to C in the form of HCO3, but I digress.


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## dennis (Mar 1, 2004)

LAKA, I "seem" to remember reading others say that angels are more sensitive to CO2 than many other fish but I am not sure nor do I know why. If that is true, I would assume some physiological or morphological reason..... but either way, you will need to use less CO2 and possibly improve you surface turbulence. A great many people are experiencing successful growth and healthy aquariums with lower than normal (by todays standards) CO2, say 15-20mg/l. The important thing is to allow the plants and tank several weeks to get used to this lower level and then make sure you are very consistent with keeping that level constant.


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## BryceM (Nov 6, 2005)

If your pH is down around 5.5 then you've probably got a pretty good CO2 concentration, even with a KH of 1. Big tanks have a small surface area to volume ratio, meaning the CO2 isn't lost to the atmosphere as easily. If you'd like to see how my system is set up you can see this link.


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## dennis (Mar 1, 2004)

I read LilLou's post to mean they are not yet injecting CO2 but have pH of 5.5... Maybe I read it wrong. If so, sorry.


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## LAKA (Feb 11, 2007)

Dennis thanks for your advice. I think i am resigned to the fact that i can't keep angelfish at 30ppm in a planted tank.I would dearly love to hear from someone out there that can tell me otherwise.
I then have 2 options. Remove the angels which i do not really want to do as they relax me after a hard day at work, or as you say lower my CO2 to 15-20ppm. My question is if i do the latter, do i need to reduce light intensity which is 3wpg at the moment?
LAKA


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## Edward (May 25, 2004)

You can double your light intensity if you lower your CO2 levels.


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## LAKA (Feb 11, 2007)

I don't know whether to take that seriously or sarcastically Edward. Now you have really thrown a spanner in the works! Please explain.
LAKA


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## Edward (May 25, 2004)

LAKA,
You are taking the 30ppm CO2 too seriously. Tell me, what bad is going to happen if you use 20 ppm CO2? 

Nothing.

The must have 30 ppm is baloney. Lower levels are actually better. No fish cruelty, more compact plants and more resistant plants to CO2 level variation. Wanna do it better? Then remove the switch, run CO2 24/7. 

You can double your light intensity from 3 to 6Wpg and run it for 6 hours, no problem.


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## dennis (Mar 1, 2004)

LAKA, I believe Edward is trying to say that you could use more light (with a shorter photoperiod) and it would not hurt anything at that CO2 level, especially if you have more WPG but for only 6 hrs or so. Several people are trying CO2 at "lower than 30ppm" with 3 wpg and having very good success. Another important thing to note is that the near inability for most people to accurately measure CO2 levels, and the variability between individuals results, leads to much confusion and difficulty. Even going by bubbles per second is hard as different regulator pressures and different bubble making devices produce varied bubble sizes (though not to drastic in general) I personally think the drop checker is a great method and even if it is not accurate, at least people are more on the same page as it adds some standardization to the measurements.

Anyway, you don't have to run out and buy more lights to use 20ppm CO2. Keep your 3wpg and run a CO2 level that does not stress the fish. Dose properly and let the tank stabilize for a few weeks. The plants need that much time to really adapt and settle into their environment.


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## BryceM (Nov 6, 2005)

Laka,

Keep in mind that the whole light/nutrient/CO2 issue is heavily debated with very few solid answers. You'll find all sorts of opinions here and from various people when you talk to them in person. The bottom line is that people are having success with a wide variety of techniques. It is also a true statement that people are failing miserably with some of those same techniques applied to slightly different conditions.

It's probably safe to say that CO2 addition is beneficial. It is also safe to say that plants require certain nutrients to grow. I'm going out on thin ice now, but I believe that conditions that results in "happy plants" tend to be "algae-resistant". Our ability to accurately measure CO2 concentration in a reproducible, broadly applicable way is almost zero. The exact particulars are as clear as mud to me, and to almost anyone who looks at these issues with an open mind. Many people have their own theories and some of them are quite certain that "their way" is best. In their own tanks, they're probably right.

My personal bias is that brief, intese mid-day lighting, moderate to high CO2 levels, frequent but small macro nutrient supplementation, frequent large micro supplementation, and a bit of luck make for a good receipe. Why do I think that? Hehe - cuz that's what I do, and for the moment, the tanks are doing pretty well.

Frustrating that there are few solid answers? Yes, but it's actually fun if you have the patience to work toward a succesful combination. Balance is the key. Light is the hardest parameter to "fine-tune" since most of us are pretty much stuck with the fixtures we purchased. The task really becomes regulating CO2 and the other various nutrients to promote healthy plants and to keep algae at bay. When a _severe_ deficiency exists, things crash hard and algae is almost always the end result.


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## LAKA (Feb 11, 2007)

In hindsight i feel that i have become fixated with 30ppm CO2. Why? Because so often i hear that the crux of problems, primarily algae is from too little CO2 ."Too much light? Nah it's too little CO2" etc etc. I have no qualms in keeping CO2 levels at a level that will not stress fish.As you all say 20ppm will still be sufficient for luxuriant plant growth and keep my angels happy.
It is a real shame there is no affordable CO2 sensor . I lnow i asked and was qouted $2000!!
LAKA


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## ed seeley (Dec 1, 2006)

I've had Wild angels in my tank with 30ppm of CO2 (measured by 4dKH drop checker) and water with 0dKH. The CO2 goes off at night and they were fine, and paired up. I've now moved the pair out to another tank and subsequently dropped the CO2 level to 20ppm (to try out the lower CO2 levels and see if there is any effect) and 1 wild angel is still doing fine in there.


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