What is the best time to test alk/ca?

[janakaybravo]

I am adjusting my two-part Randy's recipe. I'm starting slow. Should I test at night after lights go out? I'm adding it at night when halides go out. Or should I test in the morning? Or does it matter?

Thanks.

[Gudwyn]

It doesn't matter what time you test for Ca/alk. The levels don't vary from hour to hour.

pH rises during the day due to photosynthesis consuming CO2. Less CO2 at the same alk raises pH. But it's still the same alk.

Read Randy's latest article if you haven't already: http://reefkeeping.com/issues/2006-06/rhf/index.php

[Edit: if you use recipe #1 you may find certain times of day are better to dose due to pH. I like to dose in the morning before the lights come on, that's when my pH is the lowest and the buffer just raises the pH to a typical afternoon value rather than sending it off the scale. But it still doesn't matter when you test]

[Randy Holmes-Farley]

I just wouldn't test right after you add the supplement. Give it a chance to mix in first, and remember that measuring right after addition will be higher than right before the next one.

[Bojan]

How long we have to wait after adding supplement to measure ?

[Randy Holmes-Farley]

That depends on the system. Think of it as food coloring (dye) in the water. As soon as the tank is a single color, it would be mixed in. That might be less than 2 minutes in a high flow sumpless system. But it might take quite a long time to equilibrate through sumps/refugia/etc.

In my system, I expect it may take more that an hour or two for something to be fully equilibrated through my multi-tank, multi-sump, multi-refugium system.