CO2 gives a false PH? - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 08-17-2012, 06:46 PM Thread Starter
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CO2 gives a false PH?

Hey all, I'm sure this topic has come up before BUT...

I have a PH sensor, which swings from 7.4 to 6.4 depending on the time of day. First thing in the morning, after my air pump shuts off, it reads 7.4, throughout the day it reads around 6.4.

Now, I'm interested in adding some GBR's to my tank. Research tells me they like soft water down in the 6 to 7 range. How is this PH swing going to affect this fish, which I read is more sensitive?

I added some coral to my filter to buffer my water up from 7 to 7.4, so that after adding CO2, I wasn't going below 6 PH. Should I just remove this coral to soften up my water?

I'm a little confused as to what my PH level actually is as it changes so often. The fact that it changes outside of the recommended water conditions of this fish makes me think I will have a problem.

Thoughts and feedback?
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post #2 of 8 (permalink) Old 08-17-2012, 07:18 PM
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Hey all, I'm sure this topic has come up before BUT...

Yes, a few times.

I have a PH sensor, which swings from 7.4 to 6.4 depending on the time of day. First thing in the morning, after my air pump shuts off, it reads 7.4, throughout the day it reads around 6.4.

CO2 dissolves into water, this creates carbonic acid, which lowers the pH.

Now, I'm interested in adding some GBR's to my tank. Research tells me they like soft water down in the 6 to 7 range. How is this PH swing going to affect this fish, which I read is more sensitive?

PH value does NOT measure how soft the water is. GH and KH are the indicators for that. The pH swing from CO2 injection will not affect your fish UNLESS you overdose CO2 (that could kill them).

I added some coral to my filter to buffer my water up from 7 to 7.4, so that after adding CO2, I wasn't going below 6 PH. Should I just remove this coral to soften up my water?

No need to add coral or otherwise buffer water that seems perfect for what you are trying to do (keep Rams). Don't overdose CO2 and things should be fine.

I'm a little confused as to what my PH level actually is as it changes so often. The fact that it changes outside of the recommended water conditions of this fish makes me think I will have a problem.


Your pH level reflects CO2 dissolved into the water. Don't take the exact recommended pH too seriously. But make sure you don't kill your fish with a CO2 overdose.


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post #3 of 8 (permalink) Old 08-17-2012, 07:18 PM
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This is the effect of CO2 on water. It is perfectly normal, and happens to anyone that adds CO2 to their aquariums. Barring a long chemical reaction included explanation, CO2 reacts with H2O, creating a more acidic environment.

However, dont let this worry you. I keep a pair of GBR's in quite similar conditions as you, 7.5->6.5, Tap->Aquarium
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post #4 of 8 (permalink) Old 08-17-2012, 07:44 PM
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co2 will give false PH reading if KH is 0

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post #5 of 8 (permalink) Old 08-17-2012, 07:50 PM
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I'm not convinced that any pH reading is a false one. The test is pretty straightforward, so if the test says it is 4.5, the pH is 4.5, and if it says it is 8.0, the pH is 8.0. The pH is a secondary parameter, not a primary one. It depends on the KH of the water and how much CO2 is in the water, as well as how much of the other pH altering compounds are in the water. KH is a primary parameter, adding other things besides carbonates doesn't change the KH. But, pH can be changed several ways.

Isn't the real "story" the fact that pH is not important, and KH is important? I think we read so much about pH only because it is so easy to measure.

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post #6 of 8 (permalink) Old 08-17-2012, 08:52 PM Thread Starter
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I appreciate the feedback. I think the problem in my head was that I associated acidic water (PH reading) with soft water (KH & GH), but it sounds like that isn't really the case.

I keep reading "They love softer pH level of around 5.5-6.0". But as you are all telling me that isn't the whole story.

What level of GH, KH do GBR's surive in then?

Should I just aim for the standard, GH 4, KH 1 with a PH of 6 to 7? I tend to get nervous when my PH starts dropping below 6, which is why I buffered it with Coral in the first place. Well for that reason and also to keep any snails I have happy.
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post #7 of 8 (permalink) Old 08-17-2012, 09:07 PM
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My tap runs 7.5ph, 5 GH, and 1 KH. I buffer this every water change with some GH booster, CO2 drops ph to 6.5 or so, and my GBR's are happy as hell
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post #8 of 8 (permalink) Old 08-17-2012, 09:43 PM
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Totally normal, the same thing happens if you add an airstone except the ph will raise instead of lower like it does with co2.

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