Water Quality
Something in the water is likely irritating them and eventually killing them. There could be more obscure explanations, but water quality is the first thing you want to rule out because it’s both the most common cause and one of the easiest to test.
First move:
Run some activated carbon and watch the tank for the next couple of days. Carbon is cheap, easy to use, and very effective at removing many potential irritants or toxins.
If that doesn’t work:
Do a 30% water change.
If things noticeably improve afterward, remember that about 70% of whatever caused the problem is still in the tank. In that case, do 3–4 additional 30% water changes over the next few days to turn over most of the water and dilute the contaminant.
Something in the water is likely irritating them and eventually killing them. There could be more obscure explanations, but water quality is the first thing you want to rule out because it’s both the most common cause and one of the easiest to test.
First move:
Run some activated carbon and watch the tank for the next couple of days. Carbon is cheap, easy to use, and very effective at removing many potential irritants or toxins.
If that doesn’t work:
Do a 30% water change.
If things noticeably improve afterward, remember that about 70% of whatever caused the problem is still in the tank. In that case, do 3–4 additional 30% water changes over the next few days to turn over most of the water and dilute the contaminant.

