The only advise i can share would be to set him up in a quarantine tank and devote as much time and effort as you can for him...
In such a weak state, maybe do BB QT tank with a sponge filter and a cave or 2 with some small deco...
I also noticed you have cynobacteria and a few types of algae in your tank, so maybe there is other stuff in the water causing your puffer to not settle so well???
So my best guess would be keep him isolated and build up his strength through powerfeeding and cleaning up any leftover food within 30min to an hour after feeding.,,
I am also curious if you ever de-wormed your puffer when you got him??? Since Shouldenti are all wild caught as far as i know, and 99% of wild puffers will come with some form of IPs...
In such a weak state, maybe do BB QT tank with a sponge filter and a cave or 2 with some small deco...
I also noticed you have cynobacteria and a few types of algae in your tank, so maybe there is other stuff in the water causing your puffer to not settle so well???
So my best guess would be keep him isolated and build up his strength through powerfeeding and cleaning up any leftover food within 30min to an hour after feeding.,,
I am also curious if you ever de-wormed your puffer when you got him??? Since Shouldenti are all wild caught as far as i know, and 99% of wild puffers will come with some form of IPs...