I agree with rebel (in the post earlier) you need to cycle your tank. It may only take a few days....If you think it is safe for corals try putting a dead shrimp in for 2-3 days and no ammonia should form. If it does form...you have your answer; it needs to cycle. But it should only take a couple of days after the ammonia spike if you used cured live rock/water/filter media from your other tank. The filter media is key here because thats where the water flows through and touches the most. I set up a 5.5 about 2-3 weeks ago; I used half of the 5.5 gallon worth of water from my tank and the other half newly mixed. I got a cured 5.5 lb live rock, and used crushed coral that i had already. And I took the chemipure filter media from my main tank that had been there for over a month (lots of beneficial bacteria to deal with the ammonia). Then I put a dead krill in it for 2.5 days. The cycle was over in 6 days. : )