If you've had it going for 30 days, and in that 30 day period the ammonia has zeroed out i would say it has completed a cycle. The speed in which your tank cycles ammonia is dependent on the size of your bacteria colony. The size of your colony is dependent on live stock and feeding schedule. When your ammonia reach zero again, which could be a few days, Try adding one fish. you'll see an ammonia spike as the fish will be adding excrement to your tank, but in time your colony will adapt to the increase. You can continue to add fish to your tank one at a time and if youre adding any aggressive fish making sure they're added in order of least aggressive to most aggressive. When you're ready to add coral (if you're planning on going that way) definitely upgrade your testing kit. You'll need ca, alk, mag, phosphate and maybe nitrate.
