Help! If inverts have bellies, mine have all gone up!

[Fountainhead]

OK, so in the last 48 hours I've lost 4 serpent stars that I've had for two years, basically all my snails (25+), hermits (too many to count), emerald crabs (4), and porceialn crabs (6-8). If it was crawling, it's dead or dying.

I tested for copper. Nothing. Nitrates around 10, and ammonia tested at 0.2...probably from all the death and carnage. The fish are fine so far, and the Xenia and Toadstool Leather seem OK.

I've been battling dinoflagellates, which could account for the dead snails (they'd turn upside down on the sand and just die.) One thing I tried was lights out for 48 hours, and during this time the tank temp fell from the usual 79.5 to 74.5 before I noticed it. Could this temp drop have been the culprit? Could the dinoflagellates themselves be responsible? Any other ideas?

[outy]

water changes asap [large] get the old water out

ph?

could be the dino,s

[Amphiprion]

I doubt the temp was the culprit--mine have experienced swings like that in times of difficulty (storms, etc) and never had problems. I suspect there is something in the water causing them to die. I would try a substantial water change (~50% or more) just to be certain. That may help rule out certain possibilities. If that does not help, then I am not sure what would.