if he seems to be in too much pain, there are methods of "putting him down" [and no I don't mean down the toilette!]
Just something you can take into consideration. Some people dont believe in it...but if he's suffering, I think that would be better for him, as keeping him alive is more crew in my opinion [but only if he's suffering].
As he is in a smaller tank now...you'll have to change his water at least every 2-3 days. I don't know about lowing it even more if he's already in a 1 gal tank.
You can get floating devises [floating "cups" such as the breeder devises] that help him stay closer to the top while also giving him more water to circulate in. This way, you could also have another fish if you so desired...but only if in a larger tank then 1 gal.