Fish only you can get away with using Nitrates and phosphates once the tank is running. If going coral, those mentioned prior, then add alkalinity, calcium, and magnesium. Most people seem to use redsea or salifert for magnesium though.
You will want to also check your ammonia, I wouldnt recommend buying a hanna for this the cheaper API ammonia test works fine. But if you want to they also have an ammonia checker.