My new betta, Sartorius was just transferred from a bowl to a 2 gallon tank with a filter. No heater...2 gallons is supposed to be too small for a heater to properly regulate. The only issue I've had in the tank (I put 3 neon tetra and 1 corey catfish) was a major ph change went from 7.2 to 6.0 in an hour and all the fish died except Sartorius, he seemed fine. I've got the water under control mostly (with bottled distilled water and ammonia's fine and pH is just slightly high. I also put 3 more fish in with him, all of whom seem fine. Lately though, he seems to be hanging out by the top in the dark corner, he still comes out to eat but doesn't swim around the puff as much. Now I mostly see him in the evening so I don't know if he's just widing down but he has some silver coloring on his face and I can't seem to remember if it was there that much before or if it's increased. (aka is it just his coloring or is he getting a fungus). Also if he has a fungus should I treat the whole tank? And will it hurt to treat just in case it's a fungus? I'm going to try this whole include pictures thing.