cardinal fins disintegrating

[johnm]

it seems as though the fins on several of my cardinal tetras seem to be disintegrating. The ammonia and nitrite are at zero. Discus are having no problems what so ever. Happens after water changes also.(30-50% 2-3 times/week) Anyone have a clue? I just finished a h20 change and noticed one of the cards knocking on deaths door.

[1077]

Some folks suggest that cardinals are sensitive to nitrates maybe more so than other fish. I used to keep some that did poorly with nitrates above 10.