Is it normal for PH fluctuate from 7.5 to 7.9_8.0 - The Planted Tank Forum
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post #1 of 11 (permalink) Old 12-06-2019, 05:20 PM Thread Starter
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Is it normal for PH fluctuate from 7.5 to 7.9_8.0

Is it normal for PH fluctuate from 7.5 in the early morning around 7am when the lights are off, and then go up to 7.9_8.0 in the evening 9pm when the lights were on for about 8 hours.
this is non CO2 injected tank but I still do have PH controller probe still in the tank from when I used to run CO2, that's how I can tell the readings every time I glance at the tank.

thanks for your input
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post #2 of 11 (permalink) Old 12-06-2019, 08:10 PM
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Yes, perfectly normal. Your plants are taking up CO2 during daylight hours, which drives the pH up. It goes back to ambient during lights out when plants are not photosynthesizing.
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post #3 of 11 (permalink) Old 12-06-2019, 08:11 PM
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Unlikely to swing that much from simple photosynthesis night vs day and CO2... IMO

When's the last time you calibrated the probe? What is the kH of the tank water?

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post #4 of 11 (permalink) Old 12-06-2019, 08:18 PM Thread Starter
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Unlikely to swing that much from simple photosynthesis night vs day and CO2... IMO

When's the last time you calibrated the probe? What is the kH of the tank water?
probe was calibrated about 3 months ago, results were matching test strips 2 months ago.
Currently I am waiting new test strips to arrive, so I don't know the kH
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post #5 of 11 (permalink) Old 12-06-2019, 08:19 PM
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Originally Posted by ramunas View Post
probe was calibrated about 3 months ago, results were matching test strips 2 months ago.
Currently I am waiting new test strips to arrive, so I don't know the kH
What source of water do you use?

Tap / RO / Distilled etc.

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post #6 of 11 (permalink) Old 12-06-2019, 08:54 PM Thread Starter
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What source of water do you use?

Tap / RO / Distilled etc.
Just a regular tap water. I also do not add any water treatment chemicals.
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post #7 of 11 (permalink) Old 12-06-2019, 09:02 PM
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Hmm... it could be natural CO2 fluctuation causing it...

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post #8 of 11 (permalink) Old 12-06-2019, 09:14 PM
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Yup, I see similar behavior in my organic soil community tank with continuous Apex monitoring. I think DW documents this in her book.
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post #9 of 11 (permalink) Old 12-07-2019, 07:54 AM
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I have seen this in my RO tank. I made a new light and put it on the tank to test. It worked very well. Unfortunately the dimmer I ordered took longer to get than expected. At the time I generally tested the water right after the timer turned on the light. However one day I tested the water just before I went to bead. Normally I was seeing a PH of 7 in the morning or lights on. however just before lights off the PH was 9. it was going to a ph of 9 for two weeks before I recognized it and got the dimmer installed. Diming the light did solve the issue. Since the cause is most likely CO2 consumption you might also be able to minimize the change by providing more aeration to the water. I didn't notice any problems with my fish or shrimp before the PH test revealed the issue.

Note on this site many people will tell you aeration removes CO2 from the water. That is true for and aquarium with CO2 injection where CO2 levels are generally higher than in low tech tanks. But in your case aeration would put CO2 in the water. Although it might take a lot of aeration to keep the PH stable.
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post #10 of 11 (permalink) Old 12-09-2019, 05:17 PM Thread Starter
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I have seen this in my RO tank. I made a new light and put it on the tank to test. It worked very well. Unfortunately the dimmer I ordered took longer to get than expected. At the time I generally tested the water right after the timer turned on the light. However one day I tested the water just before I went to bead. Normally I was seeing a PH of 7 in the morning or lights on. however just before lights off the PH was 9. it was going to a ph of 9 for two weeks before I recognized it and got the dimmer installed. Diming the light did solve the issue. Since the cause is most likely CO2 consumption you might also be able to minimize the change by providing more aeration to the water. I didn't notice any problems with my fish or shrimp before the PH test revealed the issue.

Note on this site many people will tell you aeration removes CO2 from the water. That is true for and aquarium with CO2 injection where CO2 levels are generally higher than in low tech tanks. But in your case aeration would put CO2 in the water. Although it might take a lot of aeration to keep the PH stable.
very interesting point on aeration and CO2 addition.
I wonder is 0.5 PH fluctuation is bad for the fish or can it promote BBA growth? If not, maybe I should not worry about it.
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post #11 of 11 (permalink) Old 12-09-2019, 06:23 PM
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Quote:
Originally Posted by ramunas View Post
very interesting point on aeration and CO2 addition.
I wonder is 0.5 PH fluctuation is bad for the fish or can it promote BBA growth? If not, maybe I should not worry about it.

Fish experience some fluctuation in pH in their natural environment. 0.5 pH over half a day will only affect the more sensitive varieties.



If the pH fluctuations concern you, you can moderate them by increasing the carbonate hardness. However, this will raise the average pH.
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