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Thread: Cardinal Tetras Dieing
10-25-2012, 06:00 PM #11
21 small fish in a 30 gallon tank should not be spiking nitrates to 40 either and you should not have to be doing water changes 3 times a week. Sounds like an overfeeding problem to me.
Nitrates can also raise if the filter is too dirty and needs a rinsing. You didn't mention the filter so I would also wonder if enough oxygen is getting to the fish.