Well I took a last-minute risk when King was hanging on the surface like Rivaille did a few hrs before he died. I put him in the 10gall- aquarium.
It worked wonders! Today he's regained his color and he's very active, and he still prefers to stay at the surface (apparently he breathes a lot) he rarely ever goes to the bottom.
And actually i tested the temp of the water with my hand before putting him in, and the temperature was actually higher than that of his previous(0.5gall) tank. I think the temp's just perfect for him, not for the goldfish. (the goldfish actually stayed in the outside pond but was moved into the aquarium by my dad cuz he had parasites.)
Anyways I'll try to fix that goldfish's parasite problem using Epsom salt conservative method and see how it goes. It's also good for King's recovery i guess ^^
Happy that King made it through the night. For now. Keeping a close eye on him.
Anon's made a huge bubble nest :D it seems happy in its 0.2 gall tank, should I move him to the 0.5 or wait till I buy the 2 gall one?