If your nitrates are 100 ppm your fish are going to die. you need to keep nitrates under 40ppm or your fish will die. You need to do water changes to bring that down.
something is not right with your water. Cycling issues most likely
To be completely honest.. gourami fish are pretty weak fish are known to have this stuff happen. Not a lot of people talk about it because it SUCKS that these fish suffer through this and die. Here is a link that may help you http//gourami-fish.com/swimbladder-issues