Planted Tank Guru
Join Date: Dec 2017
Location: Elk Grove, California
If your water parameters have stayed as you list, 0/0/>10 then the issue is not with water quality. Thats pretty much perfect.
What is left over is an introduced pathogen or stress from incompatibility between or aggression within species/unknown environmental stress ( nutrition, excess fertilizers, improper use of Co2, etc...) .
You may have more than one issue happening as well, that is possible when fish become stressed and you have multiple species that have unique vulnerabilities.
Have your fish been dewormed? I would start there because this is a common malady that can go unnoticed and cause both internal issues and secondary external issues.
I would recommend treating with General Cure due to these symptoms: bloating, swim-bladder issues, lethargy. The fin rot and external issues on gourami could be secondary issues due to lowering of immunity from internal parasites.
For the external symptoms on these fish, I would dip in methelyne blue to control bacteria/fungus.