Maybe..if you do it right away..dont feed him tonite...dont want to create more ammonia for him. Id do a 100% on his tank,just to be on the safe side,if you want to wait till morning. Im not sure of your routine,but in a tank that small you should be changing several times a week,at least one full change a week as well.
If it's just SBD, then fasting for a few days and feeding him some daphnia will help. I've also read on the Jungle Fungus Eliminator that it helps SBD to, so adding that could help.
I'm sorry you aren't allowed to change the water. Do you have the cup he came in? At the very least to get him out of the water you could fill that cup with room temp water and add conditioner then put him in it. Then you can clean the tank in the morning and put him back in. I don't know if that is the best idea or if anyone would suggest you do it, it's just all I can think of to keep him in clean water for now.
his water is clean i cleaned it 2 days ago but i feed him every 2 days so i would feed him tommrow but i dont think i will now should i out him in a 1/2 gallon now? that might stress him out but i think hes fine just swimming at the top
cup he cam in? my fish cam in a bag they gave him to me in a bag with a hour to get home but i have a 1/2 a gallon i origonally had i can fill that up with warm water and dechlorinat it that im allowed to do and in the morning clean the 2.5 gallon