Shouldn't have any ammonia in your tap water I'm thinking. tet again or confirm with another test kit if possible. An ro
unit will help any tank IMO
. Check the tap for phosphates also.
Reef or fish only? I'd begin my search for live rock about now.
Have you seen or heard of Robert Fenner's "Conscientious Marine Aquarist". I'd recommend starting there before you buy or do another thing. Good book, but ignore the part about cycling with fish/damsels. Uncured live rock can do that for you much better.