fish dying (long Post)

[MitchM]

Bill, are you not concerned about the ammonia level in a 7 or 8 month old tank?
I think if it was a CO2 issue that would have been addressed by the redirection of the powerhead last night.
Ammonia will cause irritated gills and gasping for air.

I agree with you that the sandbed could be a problem if it is not being cleaned regularly.

I think that he should temporarily stop feeding his fish and do enough large daily water changes (20%) until the ammonia level is back down to zero.
Vacuuming the sandbed at that time would be prudent.