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Originally Posted by funfishies
Doing a 20% water change now should this help?
Usually that's all that's needed in milder cases. It's typically not popeye unless both eyes are affected. It will more commonly be caused from an injury. Watch for aggressive behavior from the other fish. It could have been the cause. You will need to do a few water changes over the next week for it to be properly effective though. Be sure the new SW
is properly aged/aerated for 24 hrs first though.
Soaking the foods in a good liquid marine vitamin will help the fish immune system as well. Also be sure the tang has daily vegetable grazing foods available.