My little Flounder has this same lethergy
I changed the water on Sat. and usually do every 3 days or so. He's just in a 1/2 gal tank for now. The day after I changed the water he began to just hang at the top of the water, with his little (nose?) at the water line. He too, would eat everything in site and was always so happy. Now....nothing. When I changed the water I use water that has sat for several days as well as de-chlorinator. The water is cooler that what I dump out (79*) but I don't know how I could warm it.
This time I did forget the sea salt. And now, can't remember what you told me on how much to put in.
What shall I do??