Help! BGKF Severely Bloated Belly!

It is a water filter (sry im clueless) built in the tank. I think he jumped in it or something or the current washed him in.
 
My black ghost knife's stomach has gotten bigger! the left side! I've moved it to a hospital tank but the meds are not working...he is severely constipated i suspect as there is no trace of excretement anywhere for like 7 days! HELP! HOW TO HELP CONSTIPATION? (sry im freaking out here)...
 
AquariaCentral.com