Okay so i brought my 16inch buttakofri and 11inch red devil in from my pond bc of the water getting too cold and ive noticed my red devil has what looks to be fin rot, he has gotten it before from fighting and all i did was do water changes and he healed fine but i was going to treat him this time i have melflex and i was wondering if i should add some salt and how much should i add? its a 250galling so if u guys could help it's be nice