I work at PetSmart and our 35 gallon tank has tiger barbs, clown loaches, and kissing gouramis. Only the tiger barbs are showing signs of ammonia burns and a few with, what looks like, chunks missing from their sides. All our tanks are on one system, all the other tanks are fine. We've tested our water with strips both in the 35 gallon and on the system, no signs of ammonia. Any thoughts?