Well, while he's in the cup, he's just floating in his ginormous tank. I don't really /want/ to put salt in the big tank because of the plants (now that I think about it). I like the idea of keeping him in the cup for 10 days, get him on the mend, then let him back into his big tank without salt. His fins were almost done healing from the crappy water he came in, too. :/
If you've got a small tube, you can start suction on that and get most of the water out. Leave enough to cover him, slowly add new water, wait a few minutes, and repeat 2-3 times.
If you don't have a tube, then carefully dump out most of the water in the cup into a bowl or bucket (Never over a sink since they like to investigate where the water is going and might get down the drain). Refill with water, wait a few minutes and repeat.
100% water changes was only for salt treatment. And of course not for whole tank, especially i think not all plants aquarium salt tolerant. If you think he is all better and his fins look better, he is not lethargic and eating i guess you don't have to treat him :) But i would keep water super clean though since his fins were damage and you don't want any infections.
And if you ever need to put him in the hospital tank you not necessarily need 80*. 76-80* is good temperature.
Also when fish makes bubble nest it might be that he is happy but it also natural instinct so you can't really say that fish is healthy (not talking about your fish) because of the bubble nest.
Most of his caudal fin is just... gone. The rest are crimped and mangled. He is having trouble just swimming; he has to wiggle his butt with three times as much effort to get anywhere, so I'm thinking of keeping him in his cup for a while. He's not as lethargic as last night, but he's definitely not his active self.
That'll also give me time to stabilize the pH in my big tank. It's being grumpy. Got some coral today.
As for the bubble nest, I was just glad he thought he had enough "umph" to make one.
Thanks for the help about changing his water, too. :P
That looks like it should heal relatively quickly for fin damage.
As far as those water changes, if you're keeping him in his cup, then I highly recommend those 100% daily changes or at least every other day. It might be a bit stressful for him, but the clean water will do more for him that water with high ammonia concentrations.
Perhaps when he's feeling a bit better and swimming better, you can move him up to something bigger while you get the main tank set up, but don't worry about it too much.
Rubbermaid is your friend. ;) They are cheap, and they come in every size under the sun... :) I've used them as 2.5 gallon hospital tanks, and the smaller ones as hospital tanks that can be floated in a bigger tank to keep him warm. :) Plus, a lot of the rubbermaid comes in long/shallow varieties, so you can fill it up with a gallon or so of water, but it's not very deep, so he can swim if he wants to, and chill out near the surface if he doesn't.
For what it's worth, I've had crowns looking a lot worse than yours just from getting their butt kicked by a female while trying to breed.
I've also sucked up one or two into my eHiem over the years. They are not easy to get out of the bottom of the external canister filter... let me tell you!
What I ended up doing is down sizing my intake tube for one... and adjusted the valve so it wouldn't be so strong. The ones I sucked up weren't so lucky.
It sounds like your's is going to be just fine!!
For that little cup + fin damage i would do daily water changes. I bought betta for someone and had him in that little cup at home for 3 weeks with daily water changes. He was perfectly fine. Adding stress coat is also good idea
Thanks for all the responses! Even after changing his water late last night, by noon today the ammonia was at 1ppm. D: He has several things to rest on in the 10 gal, and seems to be swimming okay, and has energy... I've already acclimated him back into the 10 gal, because I figure clean water is more important than salted, dirty water, yes?
As for healing, pieces have stopped falling off, and presumably were because there was no blood supply to them, shredded as they were. I can already see some transparent growth on the longer pieces, and over the holes.
I fasted him yesterday, and fed him some frozen daphnia today in hopes that will help with his bloating...
And yea, I've got stress coat in his water, too. :)
As a brandy-new betta owner, I really appreciate the support, and news of worse incidents turning out okay.