Mysterious pH Increase - The Planted Tank Forum
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post #1 of 12 (permalink) Old 02-13-2019, 09:04 PM Thread Starter
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Mysterious pH Increase

So, my tank water and replacement water were both 6.6. I tested them both before a water change. Now, for some reason, my tank is testing at 7.6. I can't imagine why this is happening. Does anyone have any insight into this?
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post #2 of 12 (permalink) Old 02-13-2019, 11:04 PM
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Could be due to a combination of factors: CO2 off gassing, rocks/aquascape in your aquarium that is raising your pH.

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post #3 of 12 (permalink) Old 02-13-2019, 11:15 PM Thread Starter
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CO2 is turned off right now (has been for at least 2 weeks), and the pH was at a stable 6.6 the rest of the week. I did vacuum my substrate as well, and that's all I can think of that would have disturbed anything.
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post #4 of 12 (permalink) Old 02-14-2019, 01:29 AM
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Do you have any carbonate rocks in your tank? LImestone, crushed coral, anything like that?
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post #5 of 12 (permalink) Old 02-14-2019, 01:40 AM Thread Starter
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All I have is fluval shrimp stratum with a gravel cap. I do have dragon rock, but I didn't think that could swing the pH that much. 6.6 to 6.8 is what my water comes out as, which is good for the CRS. I also have almond leaves but if anything is guess they'd be lowering it. I've tried not to add anything that would raise the pH. KH is 1 and gH is 6. Unfortunately not much of a buffer but those parameters are what were recommended for the shrimp as well.
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post #6 of 12 (permalink) Old 02-14-2019, 02:04 AM
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Yeah, at 1 dKH you've very little buffer, and I could see some dramatic pH swings. Keeping pH stable in soft, acid water without resorting to a phosphate buffer is something I've never tried. (I used to keep discus, and a phosphate buffer was more or less mandatory.)
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post #7 of 12 (permalink) Old 02-14-2019, 06:56 AM
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Test pH of the replacement water after it sat in a cup for a day or two. Using an air stone would speed it up.
The idea is to check whether your replacement water is rich in co2, which is now being de-gassed from the tank.
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post #8 of 12 (permalink) Old 02-14-2019, 07:39 AM Thread Starter
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The replacement water had been out for a few days already. I usually fill up the bucket after every water change so it will be ready by the next change. Would you expect the pH to go up or down with more time left out?

However I did go to work and come back after about 8 hours and it's back at 6.6 and the shrimp look perfectly happy. I'm a little new at this so I'm worried about adding any chemical buffers. Online suggestions vary greatly but I'm getting the overall impression that they're not a long-term solution.

Maybe I'll try doing more frequent checks to make sure I'm not missing anything.
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post #9 of 12 (permalink) Old 02-14-2019, 10:57 PM
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Quote:
Originally Posted by remaai View Post
The replacement water had been out for a few days already. I usually fill up the bucket after every water change so it will be ready by the next change. Would you expect the pH to go up or down with more time left out?
pH should go up, as any dissolved CO2 out gasses into the air.

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post #10 of 12 (permalink) Old 02-15-2019, 06:49 AM
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How long have you had the substrate, and have you already done RO, or have you used tap as well? Fluval's Shrimp Stratum really doesn't buffer that long, so it is possible that it has exhausted the buffering capabilities.

All of my buffering substrate tanks are kept at 0 dKH - you will not experience pH swings due to this. You do not want to add any sources of carbonates as this depletes the buffering capabilities of the substrate.
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post #11 of 12 (permalink) Old 02-21-2019, 08:10 AM Thread Starter
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I've had the substrate for about 2 and a half months. It could be reaching the end of its lifetime. I don't think have any carbonates in here. I have only been using RO water (remineralized back to 6-7 gH).

However, I've found that I might actually have a different problem. Once again I tested today, to find it's shot back up to 7.6+. However, the shrimp were fine; they seem happy as could be. I didn't think such a wild swing would have them looking this good. I tried to think of any other reason, and I took another sample--this time instead of from the surface, I took it from a few inches down. Lo and behold, I've got my nice 6.6 back.



These were about a minute apart (the left being the first).

So now I think that I have a issue with some kind of film at the top of my tank I can't really see, instead of a pH swinging issue. Would there be any other explanation for only the surface of my water reading that high? Or should I never be taking a sample from the surface of my water?

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Originally Posted by Darkblade48 View Post
pH should go up, as any dissolved CO2 out gasses into the air.
Would it keep rising after two days or so? I thought that would give it enough time but I might be wrong about that.
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post #12 of 12 (permalink) Old 02-21-2019, 11:02 PM
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Would it keep rising after two days or so? I thought that would give it enough time but I might be wrong about that.
Assuming you had a reasonable amount of water (and not large buckets), with decent agitation (and not just a completely still bucket of water), CO2 should off gas within 2 days, I'd imagine.

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