Taco has Swim Bladder Disorder, or so I think. He has been floating listlessly at the top of his tank, tail down and mouth up to the surface, for a whole day. He's completely vertical. He only moves if I prod him, and only then, will he struggle to move away. He has not eaten at all.
I've done frequent water changes and treated him for any possible cases of illness. I've ruled out ich and fungus at this point (which is what I thought the cause of the sudden inactivity was attested to).
I also suspect it may be ammonia poisoning, but I've done nothing to how I've changed the water before. Tian-Tian is doing fine (though battling his own case of ich again
. Freakin' fish.).
I've done all I can think of.