Don't go overboard with testing... hobby kits are not very accurate at all, you will not be able to resolve any real differences day or night, except pH as CO2 levels should change over the day... rule there is you want 20-30ppm at lights out. As for other stuff, I occasionally test nitrates, maybe once every few months, nothing else... kits are good for telling if you're way off in one area, but its often times easier to looks at the plants for signs of deficiency.chiahead said:I was curious if there is a good time to test for the tank values-No3, Po4, KH, GH, ETC. Meaning night or day, when lights are off. Just curious what the rest of you do?