I test at least weekly. But I am also heavily stocked--20 fish in a 125 Gallon. If I had 3-4 medium fish in my tank--my stocking was lighter--I wouldn't test, either. Or if I had a bigger tank with a lot more water volume. I wouldn't test. Or if I had more pothos. I have like two little sprigs in the corners, and the fish keep eating the roots. If I had a BUNCH of pothos growing in the sump, where the fish can't get at them, I wouldn't test.