My tank has been running for a month. I used the Red Sea Reef Mature Kit which seemed to work great. It knocked my ammonia down to 0 in a week. I added my first fish at week 2 (per the Red Sea program) and ammonia stayed at 0. That fish was a fire fish and he died mysteriously. I presume the cause was stress. He was curious and outgoing for the first 9 days in the tank, but after a water change his personality changed dramatically. He was ALWAYS freaking out and hiding in his cave if anyone was near the tank. The tank is right next to my desk... 2 days later he died. I did a postmortem, to the best of my neophyte abilities, and couldn't find any signs of infection or suspicious white spots. All of my parameters checked out fine, 0 ammonia, 0.013ppm nitrite, <4 nitrate, salinity was stable at 1.025, pH 8.1. To be safe I left the tank empty for a week and did a couple of 25% water changes spaced out by 3 days. My second fish was a Percula. I wanted a hearty fish this time! I got him from LiveAquaria and he was pretty neurotic from day 1. He was frantically trying to get at his own reflection for the first 2 days, without eating. The whole time I'm trying to feed him 3 times a day; 2 different pellets, frozen mysis, flake. Finally by day 3 he started to eat a little. Day 4 he ate continued to eat. Day 5, I woke up and he was dead. I did the full battery of tests: 1.2 ammonia (Red Sea), 0.031ppm nitrite (Hanna), <4 nitrate (Red Sea), 1.025 sg (Milwaukee), pH 8.5 (Hanna) He seemed to be decaying, losing color on his shoulders, so he may have died in the early part of the night. I wonder if his own decomposition contributed to the high ammonia. So my questions to you guys: What caused the sudden ammonia spike? Was it over feeding? I didn't feed much for the days that there was no fish in the tank. Could my ammonia eating bacteria have died out in that time? How do I fix this? My first thought is to do an immediate 25% water change, followed by another 25% water change for the next 2 days. Should I just do one big 50%? I'm worried about the ammonia and nitrite affecting corals and snails. Thanks!