yes tap safe is a must to remove hard metals from the water that are harmless to us but are toxic and harmfull to the fish, as well the clorine in tap water will destroy what very little good bacteria you already have in you filter media.
As well as the masive water changes i suggested earlia i would suggest you ask you LFS if you can have a small piece of mature filter media to help seed yous (simply pop what they give you in with you exsiting filter media) but do not them sell you anything like good bacteria in a bottle as this is a con and will do no good in your tank.Or ask a friend or any one you no that has a well established tank for a piece of media. Or again look on the site for mature filter doners.
Nitrates will natrally be in a heathy tank as this is a bi product given of at the end of the nitrogen cycle (were the filter turns ammonia into nitrite and then in to nitrate) Nitrate is not persay harmfull to you tank/fish in the same way ammonia and nitrite is but should be kept under say 50-60ppm as above this can be harmfull to your fish. The only way to remove nitrate is by water changes.
Have a search of the new tank bit of the forum for cycling tips and guides.
By the way how often do you feed your fish, is there alot of mess on the bottom of the tank, how often do you vac your tank.
What are you tanks stats, these will help us help you;
Tank dimension
fillter
how long have you had the tank
plants
substarte
etc....