He's in a 6gl (see betta two under my aquariums for tank specs) and the water tests the same as it always has: Ph 7.8, am 0, nitrite 0, nitrate 5.0. I do water changes weekly. I can't find the info on when I actually set this tank up but I think it's been at least six months.
For the last two days he's spent most of his time lying on the bottom of his tank. He is breathing heavily and his body now looks like it's bent into an S curve. He will swim up to the surface, gulp some air, and then he heads straight back to the bottom of the tank. His fins look the same as they always have but his body has turned pale compared to what his normal coloring usually is. When he swims he loses the S curve but once he settles back on the bottom the curve returns. At the moment his ability to swim does not appear to be affected by whatever is ailing him.
He still has an appetite but I'm only giving him one pellet in the am, and then one pellet in the pm. I just performed a water change two days ago. I have no idea what I should be doing for him at this point. I've been looking at all the diseases and illnesses and am not sure which one I should be treating for. Any assistance is appreciated!!