Since I'm using RO/DI water, shouldn't I be adding some nutrients to the water. I know I would have to for corals, but currently I only have fish and inverts. Suggestions?
No it doesn't...depending on what you use as a water supply, everything can change. You MUST check your water parameters to determine what your tank needs. Do not become complacent with your water. What are your current parameters now?
I don't even test for minerals such as calcium becuase I do not yet have corals. The five elements which I test for are as follows:
Ammonia: 0
Nitrite: 0
Nitrate: <10ppm
PH 8.2
Salinity/SG: 1.024