One of my bettas, Willie, has just started acting very lethargic, hanging out at the top of the tank. He doesn't look constipated, and will swim down, but he just sits there, without even the pectoral fins moving much. (I have had other bettas that were constipated and with slight swim bladder problems, and they sort of bobbed at the top.) All the other bettas will swim up and down, or if they are just in one place, even the pectoral fins are moving. I currently have 12 bettas in separate tanks, they get the same treatment and food, and are doing fine.
He is in a two gallon hex tank, water temp about 78 (room temp), I just cleaned the tank today and put 1/2 tsp aquarium salt/gallon in. I use tap water treated with declorinator drops. We usually fully clean the tanks once a week. There are also live plants in the tanks.
Any suggestions or symptoms to watch for? He just doesn't seem right.
(Amazing how when you get to know your fish you just know when something isn't right!)