I would say the first thing you need to do is give him some pedialyte baths immediately. 2-3 baths a day for a duration of about 5 minutes each time would be sufficient. I use an eye dropper for this and just steadily drip the pedialyte on his back. If you have any cultures, I'd also put in a good amount of springtails into his tank in case he'd like anything smaller than ff's to munch on. Good luck with him, I hope he pulls through.