pH - Diurnal variations in my tank

[JulesH]

Hi David

I have a 320 liter tank. I add about 300 to 400ml of Kalk through a stirrer and I get a peak pH of 8.74 during the day. Frustratingly I am not sure if I believe the Apex pH probe, although it does calibrate. Most people it seems struggle to get their pH above a certain point, I seem to have the opposite problem!

 

[Randy Holmes-Farley Verified Community Expert]

As I understand the chemistry of Calcium hydroxide, the raising of pH stops soon as you stop doing or very nearly so?

Correct. Any pH rise stops after you stop adding it. The pH may begin to drop back as more CO2 enters the aquarium.

That is why folks use it continually, rather than a once and done.

 

[Randy Holmes-Farley Verified Community Expert]

When I'm out of town for work for longer than ounds like mine3-4 days my indoor CO2 reports at 380-400ppm. My PH seems to cap out at 8.55 with pretty heavy kalk dosing. It reliably gets to that exact point and flatlines trip after trip (using a neptune PH probe). During this time my diurnal swing goes down to ~8.35ish

Sounds like the same range I got in a home with leaky windows.

 

[Randy Holmes-Farley Verified Community Expert]

Hi David

I have a 320 liter tank. I add about 300 to 400ml of Kalk through a stirrer and I get a peak pH of 8.74 during the day. Frustratingly I am not sure if I believe the Apex pH probe, although it does calibrate. Most people it seems struggle to get their pH above a certain point, I seem to have the opposite problem!

Which should tell you something: don’t believe it without a lot of verification.