How much c02 is too much? - The Planted Tank Forum
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post #1 of 11 (permalink) Old 03-15-2016, 01:20 AM Thread Starter
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How much c02 is too much?

How much c02 is too much for fish?

I ask this because I usually run about 3 bubbles per second of c02 and my aquatech c02 regulator decided that wasn't enough and adjusted itself to about 8-10 bps. I noticed my fish weren't acting odd so I let it stay there for a few days. I just checked my ph and it was 6-6.4 (6 when held against a white background and 6.4 held against the white of the color chart; api master test kit). My kh is currently 5. I checked the chart and it suggested somewhere between 59 and 150 ppm of c02 depending on which ph reading I went with. I have read so many people talking about killing there fish at 50-60 but never really got a consensus about how much is too much c02 for a fish.

If my c02 is really this high the only thing I can think of is my plants producing enough oxygen+using an aqua clear hob (no splash)+using an Eheim surface skimmer are helping make it so the fish don't suffocate. Any thoughts?
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post #2 of 11 (permalink) Old 03-15-2016, 01:31 AM
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You KH kit may be off or your PH probe may need calibrating check you KH that's what really matters when it come to ph and co2.
If your KH is one you can safely have like 4.8 ph but the fish will not be thrilled.If you have Hi O2 this will allow lower ph as well but recommendations i've seen is raise KH and lower Co2 effectively heightening PH so everything is happy.
Google KH CO2 chart

My Tank had 4.8 ph the other day and my fish and shrimp are fine but my KH is 1 and i run a sump with surface skimmer no O2 at night
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post #3 of 11 (permalink) Old 03-15-2016, 01:59 AM Thread Starter
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Originally Posted by SwampGremlin View Post
You KH kit may be off or your PH probe may need calibrating check you KH that's what really matters when it come to ph and co2.
If your KH is one you can safely have like 4.8 ph but the fish will not be thrilled.If you have Hi O2 this will allow lower ph as well but recommendations i've seen is raise KH and lower Co2 effectively heightening PH so everything is happy.
Google KH CO2 chart

My Tank had 4.8 ph the other day and my fish and shrimp are fine but my KH is 1 and i run a sump with surface skimmer no O2 at night
The c02 levels I got were from the kh/c02 chart. When I was using ro water my kh was 1-2 and when I switched it over to my tap water it has been a rock solid 5 with a gh of 11. I get that you can get away with different ph levels as long as the kh relationship is on point. I know testing kh can be tricky because of inaccurate tests but this one consistently measures the same for known kh's. I was just really surprised at the ph and the possible c02 concentrations being higher than others have reported being safe.
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post #4 of 11 (permalink) Old 03-15-2016, 03:27 AM
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The chart that shows ppm of CO2 vs KH and pH works fine only for water that contains nothing affecting pH and KH except carbonates (bicarbonates) and CO2. Water in an aquarium almost never meets that criteria, so the table almost always gives a ppm that is much higher than it really is. The only accurate CO2 measurement you can make, using KH and pH of the tank water is when you keep the KH constant and measure the change in pH from when you have no added CO2 in the water and when you have injected CO2 into the water. When you measure that difference you have added 10 to the change in pH power times the ppm in the water before you added CO2. It is believed that the ppm of CO2 from the atmospheric CO2 is about 3 ppm, so if you add enough CO2 to drop the pH by 1.0, you have 30 ppm of CO2. This method is also inaccurate when you use a test kit that requires you to match the color of the sample water to a chart of pH vs color, because it is extremely difficult to judge that color close enough to get any accuracy. (If you think you have dropped the pH from 7.0 to 6.0, you may really have dropped it from 7.1 to 5.9, or from 6.9 to 6.1. The first means a ppm of 48 and the second means a ppm of 19. That is a huge uncertainty!) And, the ppm of CO2 from the atmosphere can be at least as low as 2.5 or as high as 3.5, so that makes the uncertainty be as much as 16 to 55 ppm.

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post #5 of 11 (permalink) Old 03-15-2016, 03:37 AM Thread Starter
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Originally Posted by Hoppy View Post
The chart that shows ppm of CO2 vs KH and pH works fine only for water that contains nothing affecting pH and KH except carbonates (bicarbonates) and CO2. Water in an aquarium almost never meets that criteria, so the table almost always gives a ppm that is much higher than it really is. The only accurate CO2 measurement you can make, using KH and pH of the tank water is when you keep the KH constant and measure the change in pH from when you have no added CO2 in the water and when you have injected CO2 into the water. When you measure that difference you have added 10 to the change in pH power times the ppm in the water before you added CO2. It is believed that the ppm of CO2 from the atmospheric CO2 is about 3 ppm, so if you add enough CO2 to drop the pH by 1.0, you have 30 ppm of CO2. This method is also inaccurate when you use a test kit that requires you to match the color of the sample water to a chart of pH vs color, because it is extremely difficult to judge that color close enough to get any accuracy. (If you think you have dropped the pH from 7.0 to 6.0, you may really have dropped it from 7.1 to 5.9, or from 6.9 to 6.1. The first means a ppm of 48 and the second means a ppm of 19. That is a huge uncertainty!) And, the ppm of CO2 from the atmosphere can be at least as low as 2.5 or as high as 3.5, so that adds still more uncertainty.
Yeah I agree that it is not a truly accurate way of measuring co2 concentrations. What I was looking at is three things; ph/kh chart, drop checker (goes from very dark green to very yellow), and ph drop from non injected water to injected 7.8 (api kit closest I could figure) to 6-6.4. When I put all three together it gives me the closest way I can measure. I would say it's probably more likely to be 6.2-6.4 +\-
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post #6 of 11 (permalink) Old 03-15-2016, 02:56 PM
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Too many variables involved to really test on paper. Watch your fish. When they are gasping at the surface then you've found out how much is too much!

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post #7 of 11 (permalink) Old 03-15-2016, 04:50 PM Thread Starter
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Originally Posted by lksdrinker View Post
Too many variables involved to really test on paper. Watch your fish. When they are gasping at the surface then you've found out how much is too much!
Yeah this is why I left the co2 so high. The fish didn't seem to mind at all. Shrimp kept molting fish weren't gasping and schooled nicely. At a minimum it looks like my co2 is about 50-60 ppm. I don't want to throw bad info out there but it looks like as long as you keep the oxygen levels high enough you can really crank the heck out of co2.
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post #8 of 11 (permalink) Old 03-15-2016, 04:58 PM
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Shouldn’t we be rather asking, How much CO2 is enough?


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post #9 of 11 (permalink) Old 03-15-2016, 05:33 PM
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These last two post combine my beliefs, make sure there is enough oxygen first (adding CO2 actually increases O2 with enough plants in), then you can pour on just as much CO2 as you can match with lighting and fertilisers.

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post #10 of 11 (permalink) Old 03-15-2016, 06:40 PM
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Originally Posted by Edward View Post
Shouldn’t we be rather asking, How much CO2 is enough?
The answer to that depends on your definition of "enough". And, of course, the answer to "how much is too much" depends on your definition of "too much".

Even with low light CO2 is a good addition to the water. Plants grow faster with CO2 at any light level. Faster growing plants are less likely to suffer algae attacks.

If you have no fish or other fauna in your tank "too much" is a lot larger number than if you do have fish or other fauna.

I believe the optimum amount of CO2 can be determined for any planted tank, by slightly increasing the CO2 bubble rate, making sure there are adequate concentrations of all of the other plant nutrients, and watching for improvements in the plants for a few days. If there is improvement, repeat until there is negligible improvement, and you have reached the optimum bubble rate. If the fish show any signs of suffering from the added CO2 you have passed the optimum bubble rate.

Now, since the plants are growing better they may increase their mass enough to need a higher bubble rate of CO2, so I suppose this test would have to be repeated as the plant mass changes.

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post #11 of 11 (permalink) Old 03-15-2016, 09:22 PM Thread Starter
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I agree with how much is enough (in terms of a thought process). My original question of how much is too much was because of my immediate experience in the original post and not really finding any clear answers. I assume like someone else had said that there are too many variables that come into play for a precise answer (even though you could probably generize the answer by saying "at the point that it effects a fishes ability to take in oxygen"). I think I may also be able to get away with higher co2 levels because I recently did a rescape and added new plants which may be absorbing more carbon now that their roots are established and are starting to grow quite a bit. But I guess that that may not matter because the concentrations are still higher regardless of carbon uptake.
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