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pH, plants & light


Guest Mr Grump

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Guest Mr Grump

I have a Seneye unit which takes tests every half hour. I have noticed over time that my pH will increase at night & reduce during the day. The extent of the changes is from pH6.8 up to pH7.0 & down again on a constant daily cycle which peaks around 09:00am & dips at around 23:00pm. My water changes every 2 days will boost the pH back to around 6.9.

I am assuming that the cause of this cycle is photosynthesis from the plants, in that during the day they will produce oxygen & at night absorb oxygen & produce CO2 which is alkaline. My fish are fed 3 times per day (morning, lunch, night) with protein rich food, which I would have expected to produce more alkalinity during the daytime, but I am not seeing this.

Could the plants have this much effect? The tank is not heavily planted. The lights are on for only 4 hours per day.

(The free ammonia is an almost flat line of between 0.003ppm & 0.010ppm at a peak.)

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I believe CO2 is acidic when dissolved in water, carbonic acid, so would think that pH should drop with the lights off, if green plants/algae were causing the changes. That Seneye monitor sounds really cool!

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Guest Mr Grump

@HH

That is what I was thinking, I would expect to need many plants for them to have much effect at all.

@tele

My water is from an HMA filter aged for a day in a food safe barrel & aerated. It's a constant pH7.

@schoolie

Ahh, I thought that CO2 was alkaline. There goes my theory! :(

I have slight brown algae issues - no green algae. My Nitrates are around 5-10ppm, Phosphates out the tap are 2ppm & I have 2 Phosphate absorbing cartridges in the tank to try to keep them under control down to 0.5ppm.

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In a planted aquatic area, ph rises at day time and decrease at night because of photosynthesis.

O2 raise the PH, CO2 decreases it.

It's perfectly normal. To avoid too much "violent" Ph swing (IMO, it's not your case), you may want a minimum KH of 4 (70 ppm).

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My pH is decreasing during the day. :(

My KH=3? & GH=3?.

This is too low, Nick, for both your plants and for your goldfish. (Other fish like discus is another matter.) Moreover, this low kH is barely good enough to maintain your BBs.

You really need to raise both to 100-150 ppm, or 6 degrees.

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@dnalex

Sorry, I should have been more precise. This is in my Discus tank. The small number of plants in the tank are Amazonian.

@schoolie

There is no temperature swing, it is a constant 82°F with a lowest of 81.5°F as the two heaters cycle on & off. Water changes are temperature matched.

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