PH changes night and day - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 3 Old 04-20-2012, 07:38 PM Thread Starter
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PH changes night and day

Does anyone know why the PH changes at night and in the morning it will change again?

This is the second time that I have tested at night and my PH is 7.9 and when i test again in the morn it will be about 7.5
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post #2 of 3 Old 04-20-2012, 07:58 PM
if you are using api liquid test make sure you keep it under the same light source because that can change the resul to your eye!
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post #3 of 3 Old 04-21-2012, 11:59 AM
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This is the diurnal fluctuation in pH which occurs in nature and in the aquarium, especially one with live plants. It will not be significant (unless something is way out of balance) to harm the fish, as I said it occurs in nature too.

One should always test pH at approximately the same time each day, due to this flucutation. This will allow you to see any changes from day to day.

It has to do with CO2 and carbonic acids, the buffering (KH or Alkalinity) of the water, and the GH (general hardness). Rather than go into all this, have a read of this article which may provide the background; if you have further questons from that, ask away.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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