Instruct: Classify a given review into positive or negative sentiment.
Query: Not so sure.. reef was not happy.

I'm not quite sure how to pinpoint the problem... but I went through this whole tub and my reef was not really happy. (55 gallon tank) My trumpet, frogspawn, and hammer corals were all receding and I couldn't figure out what was going on. Fish have all been fine though. I do big water changes. The first water change I did with a different salt, things started looking better. Another 50% water change later, and things are bouncing back to life. Just my 2 cents. Not a good experience for me.