Hey, I have an opaline gourami who was in a tank with a rainbow shark who passed away. I quarantined the gourami for a couple days and had the water checked, the water showed up acceptable on all the tests so when it seemed the gourami was doing okay in quarantine I added him to my 45 gallon. He seems happy most of the time, swimming the length of the tank regularly, but also is sometimes going all the way to the bottom of the tank and sitting on the bottom. I don't know if he's just out of shape having so much more swimming room going from a 10 to a 45 gallon tank or if there's something wrong with him, his outwards appearance is fine except for the bottom of his stomach is a bit brown, first off does anybody know if this is an illness and 2nd off would aquarium salt help? Thanks