If he looks bloated change water and use Epsom salt.
In a bath or tank since your in hospital tank already.
It could be constipation(hoping..)
If something bacterial is setting in then it is not a good sign as secondary infections arrive while main infection is still strong usually.
I am not sure what meds but some antibiotics can help supposedly help with bloat(dropsy) so just stay on task with your meds.
As bad as it is to see secondary infections the treatment that is most successful usually is the treatment for first /original issue.
Good luck ,and keep us informed or shout out!