If your betta is kept in a bowl or tank that holds two gallons of water or less, change a third of the water every 3-4 days. If your betta is kept in a larger aquarium, change 10% to 25% of the water every 2-4 weeks. [1] X Research source
Dump out all of the water in the fish tank, remove all rocks and decorations, and rinse them with clean water. Using a paper towel, scrub the inside walls of the tank. Put the rocks and decorations back in the tank and fill the tank most of the way with bottled drinking water or pretreated tap water before putting your betta fish back in.
If the pH is too high, filter water through peat moss before putting it in the tank. If the pH is too low, add baking soda or shells to the tank. [4] X Research source
Put ampicillin in the fish tank and switch out the water every third day. Administer the medicine until a week after your fish’s popeye has gone away. [8] X Research source If you catch the popeye early enough, you can use erythromycin, minocycline, trimethoprim, or sulfadimidine, which are all antibiotics typically used to treat fin rot.
In more severe cases, one of the betta’s eyes might decay and fall off during the healing process. If this happens, keep your betta isolated permanently.
