Why did my catalytic anemone die?

Question

my ammina is 0.50, my p.h is between 8.2-8.4, nitrite is 0.50, and nitrate is between 40 and 80 my salinity is 32 (1.024) and i have feed them brine shrimp i have some urchins and about 5 fish the tank is a 20 gal long

Answer 1

Those readings of ammonia, nitrite and nitrate are a sign there's a problem with your water quality. Ammonia and nitrite must be at 0 and that nitrate is just as lethal at readings over 20ppm. Creatures like anemone's are highly sensitive to these things. That's potentially a lot of fish for a 20 gallon depending on species and urchins need much larger tanks.