I would go ahead and start a treatment..If he is bloated or having any buoyancy problems use Epsom salt 2tsp/gal-If its just the fins and lethargic use aquarium salt. Both will help with the fins....but aquarium salt is better for the external problems.
Best to QT in a small bare container that can be floated in the heated tank to maintain temp in the 76-77F range for treatment...Attach it to the side so it doesn't sink and cover with a lid so he doesn't jump out...Turn off the light for the first 24h.
Premix some treatment water in a 1gal jug of dechlorinated water. Add aquarium salt or Epsom salt 2tsp/gal and a tannin source if you have one-either IAL (1lrg crushed/gal
) or dried Oak leaf (20crushed/gal
) Let this steep for 30min so the tannins can start to release and salt to dissolve....Shake well before use.
Using this premixed treatment water-make 25% water changes every 15min for 1 hour today....You can dump half the water out of the Qt he is in and just add the Tx water until full-then repeat until he is in 100% of the treatment water over that period of time.
He needs to stay in this treatment water in the Qt for the duration of the treatment period of 10 days.
Tomorrow start 50% daily water changes with the premixed treatment water.
If you added a tannin source-the water should look darker every day
If you have access to mosquito larva offer several rinsed several times a day to boost protein intake to promote healing and strong immune response.
You can lace/roll the pellets in fresh crushed garlic juice to stimulate appetite if you don't have mosquito larva...sometimes it helps and sometimes it doesn't.....He can go for some time without food, however, as you already know.....nutrition is really important to support the immune response and promote healing....
Good luck and keep us posted.......sometimes they just need some time in a dim lit quiet location....