Effects of co2 on ph? - The Planted Tank Forum
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post #1 of 5 (permalink) Old 10-19-2016, 04:22 PM Thread Starter
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Effects of co2 on ph?

I know co2 drops ph but will the ph go up when my co2 is turned off? Will it continue to drop until I do a water change?
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post #2 of 5 (permalink) Old 10-19-2016, 04:53 PM
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The pH will drop when you inject CO2 and go up when CO2 is consumed or escapes the aquarium. How big the change is depends on the KH and amount of CO2. CO2 is not the only thing that can drop or raise the pH in an aquarium.

Typically one adds X ml (at normal atmospheric pressure) / hour for as long as the light is on. After a couple of days you will notice that you get the same pH at the end of the day. Of course when you make a water change, the water you add will have a different CO2 concentration, depending on your tap.

This thread here has more details: CO2/pH/KH table - Aquarium Plants - Barr Report
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post #3 of 5 (permalink) Old 10-19-2016, 04:54 PM
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Whenever there is CO2 dissolved in water, a small portion of it is in the form of carbonic acid, so it drops the pH. When the CO2 outgasses, the carbonic acid becomes CO2 again, and it, too, outgasses, so the pH goes back to the original value.

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post #4 of 5 (permalink) Old 10-23-2016, 09:00 PM
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It is funny....in reef tanks we use CO2 scrubbers to remove CO2 and potentially raise PH.....in planted tanks we add CO2. Now only if I can figure out a way to pull from one and give to the other :-)
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post #5 of 5 (permalink) Old 10-23-2016, 09:07 PM
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This is what makes the drop checker work to let us estimate what amount of CO2 we are maintaining. The drop checker is just a modified PH test that should change color at the level we expect.
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