Ph Swing - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 07-23-2012, 02:47 AM Thread Starter
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Ph Swing

I did a fifty percent water change on my aquarium today the ph was around 6.8
I used RO water to fill it back up and the ph went up to over 7.8! So I checked the ph of the RO water and it was below 6.0, How did this happen?
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post #2 of 13 (permalink) Old 07-23-2012, 03:00 PM
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What kind of ph test kit are you using?

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post #3 of 13 (permalink) Old 07-23-2012, 10:11 PM Thread Starter
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API Test and adjuster kit.
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post #4 of 13 (permalink) Old 07-24-2012, 01:02 AM
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Are you adding CO2 to the tank?
What were the GH, KH and TDS before and after?

What is in the adjuster kit and why use it?
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post #5 of 13 (permalink) Old 07-24-2012, 01:32 AM
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Quote:
Originally Posted by Zuni View Post
I did a fifty percent water change on my aquarium today the ph was around 6.8
I used RO water to fill it back up and the ph went up to over 7.8! So I checked the ph of the RO water and it was below 6.0, How did this happen?
RO water at under 6.0 pH? That don't sound right. Should be around 7 pH. But anyways when doing a water change of that amount your pH can swing and depends on how well your substrate buffer it change lower the pH back but give it some time.

Also Co2 can make a difference. My tank is injected with Co2 so when I do a big water change the pH will go up but that is why I don't check pH right after I change water. I wait for the water to settle in first maybe about 1 hour then I'll do all my testing (GH, KH, pH).


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post #6 of 13 (permalink) Old 07-24-2012, 03:07 AM Thread Starter
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Originally Posted by Diana View Post
Are you adding CO2 to the tank?
What were the GH, KH and TDS before and after?

What is in the adjuster kit and why use it?
Don't have the equipment to check GH, KH, or TDS.
Yes I'm using pressurized co2.
The kit just has ph up and ph down, but I Don't use them.
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post #7 of 13 (permalink) Old 07-24-2012, 03:12 AM Thread Starter
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RO water at under 6.0 pH? That don't sound right. Should be around 7 pH. But anyways when doing a water change of that amount your pH can swing and depends on how well your substrate buffer it change lower the pH back but give it some time.

Also Co2 can make a difference. My tank is injected with Co2 so when I do a big water change the pH will go up but that is why I don't check pH right after I change water. I wait for the water to settle in first maybe about 1 hour then I'll do all my testing (GH, KH, pH).
RO/DI water. I just checked the ph about 5 minutes ago, still above 7.8. I'm afraid to do another water change, might kill my fish.
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post #8 of 13 (permalink) Old 07-24-2012, 07:06 AM
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Don't have the equipment to check GH, KH, or TDS.
Yes I'm using pressurized co2.
The kit just has ph up and ph down, but I Don't use them.
If you are using Co2 then your water should be acidic. Closer to pH of 6 or even lower. Because the chemical reaction when Co2 combine with H2O it creates carbonic acid which will lower your pH. You sure whats in your bottle is Co2 not air?


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post #9 of 13 (permalink) Old 07-24-2012, 01:29 PM
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Knowing what KH you have is even more important than pH. If you have at least a few degrees of KH your pH will not swing as wildly. Also, is it possible you added the RO waste water instead of the filtered water to the tank when you did the water change?

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post #10 of 13 (permalink) Old 07-24-2012, 01:31 PM
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perfectly pure RO water has a pH of 7 and no buffering capacity. BUt a slight diffusion of CO2 from the air will easily lower the pH. But since there is no buffering capacity, if you mix RO with any buffered water, then the system will reach a pH between the two, but close to the buffered water pH.

..now, as to why the pH was above either of the two when you mixed them, that points to either test failure, or user error on the testing....or, if your tank had a lot of disolved CO2, the turbulent mixing of weakly buffered total water, could have outgassed CO2 causing a raise in pH.


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post #11 of 13 (permalink) Old 07-24-2012, 10:07 PM Thread Starter
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Knowing what KH you have is even more important than pH. If you have at least a few degrees of KH your pH will not swing as wildly. Also, is it possible you added the RO waste water instead of the filtered water to the tank when you did the water change?
I thought about that, so I checked the water coming out of the hose, It was below 6.0.
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post #12 of 13 (permalink) Old 07-24-2012, 10:09 PM Thread Starter
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perfectly pure RO water has a pH of 7 and no buffering capacity. BUt a slight diffusion of CO2 from the air will easily lower the pH. But since there is no buffering capacity, if you mix RO with any buffered water, then the system will reach a pH between the two, but close to the buffered water pH.

..now, as to why the pH was above either of the two when you mixed them, that points to either test failure, or user error on the testing....or, if your tank had a lot of disolved CO2, the turbulent mixing of weakly buffered total water, could have outgassed CO2 causing a raise in pH.
The co2 had been off the previous day, and was on for about 3 hours the day I did the water change.
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post #13 of 13 (permalink) Old 07-24-2012, 10:25 PM
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CO2 on for 3 hrs is enough to reach equilibrium.


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