I am suspecting that the thiaminese (sorry about spelling) enzyme in the guppies and rosies could be causing a B1 deficiency and explain the seizures. I know he is a picky eater...but if he makes it through this...I would recommend starting to feed him store bought tilapia or rainbow trout or silversides, or worms, or pinkies. The reason for not feeding fish with lots of thiaminese in them is that it can cause this deficiency and I have heard of members who had snakes that developed seizures from it. If you decide that it is hopeless, I would probably try to make him comfortable as possible until he passes or go with the dry ice that Steve suggested. Do you have a vet?