When to test water?

[Jen]

I was reading in a book of mine that the pH of the water changes throughout the day, so in order to get an accurate reading, when should I test it?

Or is that even true?

 

[breezer40]

I have never noticed any change in my PH and I test at different times of the day.

 

[jimbooo]

that will only happen if you have a very low KH reading ie no buffering capacity.

my ph stays pretty constant and KH if i remember correctly is about 4/5 ppm ish

 

[houndour]

I read that if you wanted to get the 2 readings, you take it in the morning and at night.

So just before lights go on, and just before lights go off. I imagine that would give the 2 extremes. I only really test in evening now. But when I was first testing when I first added CO2 my pH would be 6.4 to 6.7 Cant remember which was evening and which was morning tho.

 

[George Farmer]

In a heavily planted tank generally pH will be lowest in the morning and highest in the evening.

During the day plants produce O2 and consume CO2 during thus raising pH.

At night the plants (and fish) produce CO2 and consume O2 thus lowering pH.

This effect is exaggerated if one injects CO2 24/7. This is why CO2 night shut-off valves/pH controllers are employed by many planted aquarists.

If you measure your pH just before lights on and again just after lights off you may see the difference.

Simple eh?