He's in a 30-gallon tank, by himself. I've not done anything new or different to the tank. He started looking a bit funny yesterday, standing on his head, but then he'd be fine. Today several times I've thought he was dead, but then he would appear to be okay again.
The SG for this tank is approx. 1.010 -- so on the low side, but he's been doing fine and really made quite a recovery from when I first got him.
I tested for ammonia, which was 0.3 mg/L and also tested for nitrite which came out as 0.6 mg/L.
I'm not sure why those numbers were up, but I've just done a 75% water change to help things.
I am really worried about him, I've grown very attached to him and was so happy that he'd recovered from his eye injury so well. That appears to be all healed up and I thought he was fine.
Anyone got any ideas?

