well the cycling process takes longer than that. If you see my thread, you'll see that I set my tank up on 2/1. I think you're just barely going through your ammonia spike right now. Give it time, just be sure to do 50% WC (w/ water conditioner) every other day to keep the ammonia levels low while your tank cycles.
Oh I just saw you have a brackish setup. Dont know much about brackish water but I think it should be the same. If you cant do the WC's, you might lose some fish as the ammonia gets higher. I didnt lose any of mine, but it is a possibility...