I have two bettas in a divided ten gallon tank, and they keep getting fin rot. I know that fin rot is caused by bacteria in dirty water, so I always try to keep my tank as clean as possible. I do a 50% water change weekly, vacuum the gravel, rinse the plants, rinse filter media in old tank water, add betta safe and aquarium salt, check the ph and make needed adjustments, make sure the water is the same temperature as before, and add my bettas.
I think the problem is from my gravel not being cleaned thoroughly enough. Does anyone have any suggestions on how I can keep a cleaner tank or clean my gravel better?