sick angel

Not a week noway.

Do you know what kind of fungus? How is the tank he/she was in?

I would certainly try and keep the QT tank as stable as possible (heat, light, parameters, etc.) If you don't want a filter, doing a lot of mini water changes and maybe a couple of air stones could help, but I would strongly advise getting a circulatory system for this. Especially with an Angel.

Are you treating him for the disease?

Need more info

you need to check your water quality and the conditions the angels are in..fin rot does not just happen..it is generally a result of water that is 'less' than prime.

in good water conditions the fish are not as apt to be stressed and less prone to infections.

as long as you have (seeded)filtration running in the hospital tank and do daily water changes the fish should be fine..are you using meds
you want to maintain a very clean tank for the hospital tank.if you are dosing meds follow the directions on the meds. note..many meds for 'fin rot' will wipe out your seeded filter..you will need to stay on top of the water in these cases.