My tank has been cycled for three weeks now. At the end of the fishless cycle Nitrates were >75 (Hanna). Almost 100% water change and level has remained around 10 since then. Phosphates have always been 0.0 (Hanna ULR). All other parameters are WNL’s. The 150 gal tank has eight small fish. How do I decide when to start water changes? I am set up for automated daily changes whenever I decide to start. Thanks in advance.