Once you get some experience you can tell by looking at your corals. For what it's worth I test maybe every 2-3 months and that's only Ca Kh and Mg. I know exactly what goes in my tank. I haven't owned a nitrate kit or any other test kits for many years. Call it cockiness er whatever you so choose. I call it tank OCD. My tank is in my main living area of my home and I try my hardest to keep it a piece of art rather than an eyesore. If not my wife wouldn't allow it there.
