I've had 5 fish die recently, and it's a mystery to me.
I tested my tank earlier today and it had 0 ammonia, 0 nitrites, 20 nitrates, a Ph of 7.6 and a temp of 74.
It's a 60 gallon community tank with molly's, angelfish, red-eye tetras, bala sharks, neon tetras, gouramis, siamese suckerfish...