my angel died

[asherah]

I don't know why. He was fine last night. Eating and swimming around like usual.
He has a few small nips out of his tail. Maybe the clowns killed him? I've never seen them have problems before.
The only thing new I've done is to add snails on saturday.
The ammonia is 0
nitrate is less than 40ppm - test doesn't go any lower,
and nitrite is less than 0.5ppm - test doesn't go any lower.
ph is 8.2
salinity is 1.024

any ideas?
asherah