When your ammonia and nitrite levels are at zero, and you are showing some nitrates, then your cycle is complete. I've never done a fishless cycle, so I think the nitrates are probably very high. If your tank is cycled, do a massive water change, like 75%, refill the tank, and add your fish. Make sure your nitrate level is below about 10 before adding your fish. 75% is a guess, and you may need to change out more than that to get the nitrates down to below 10.