Last week my tank was 3.5 months old. I have 2 clowns and 1 starry blenny. Everything was going well despite the ugly stage forming. I went to my LFS to buy clean up crew, and bought a dozen or so snails/hermits, and also a short spined black urchin. They also recommended me to dose seachem stability. I have been consistently dosing stabiltiy as the directions say, and this morning all of my fish are suddenly on the sandbed breathing heavily. I noticed a couple crabs have died, and the urchin is losing alot of spines. I tested ammonia with red sea kit and it was around 0.2. First time it has increased since the initial cycle. Im sure it spiked because of the deaths, but what caused the sudden crash? My temp is consistently 78 and my salinity is 1.024. I performed a 20% water change. What can I do?