I can't seem to keep Cory Catfish. This last batch of 4 died in two days with all their barbells missing.
Ammonia 0, Nitrites 0, Nitrates 5
Tank cycled a year and a half ago. 1/2 planted, 55 gal, 80°, 50% water changed 2x's a week, more if newly introduced stock
I am assuming some kind of...