Unfortunately that's your problem. Without enough water flow and space, doesn't matter if they get along, they will be stressed. Filtration also adds air into the water and with a over crowded tank, they are having much more ammonia,co2, nitrate,etc. They are stressed in some way, even though they get along.
I would try to get them in a bigger tank. First, while treating them with the salt and heat. As long as you stay under 10 saltinity, pretty sure it's 1.008 gravity (will double check gravity number) they should be fine with little issues for short periods of time.
I have my tank at 1.004 all the time, almost brackish and my fish are great. I have some fish that will go brackish when they get older. I had a nice problem 4 weeks ago with extremely sensitive fish, all did great. Knife fish, rope fish, freshwater moray eel, etc.
My tank got it because of a new addition I put in the tank, looked health in store got home wasn't, and like a dumby should have brought it back but didn't. Best practices, have a separate tank for qaurntine.
I would try to get them in a bigger tank. First, while treating them with the salt and heat. As long as you stay under 10 saltinity, pretty sure it's 1.008 gravity (will double check gravity number) they should be fine with little issues for short periods of time.
I have my tank at 1.004 all the time, almost brackish and my fish are great. I have some fish that will go brackish when they get older. I had a nice problem 4 weeks ago with extremely sensitive fish, all did great. Knife fish, rope fish, freshwater moray eel, etc.
My tank got it because of a new addition I put in the tank, looked health in store got home wasn't, and like a dumby should have brought it back but didn't. Best practices, have a separate tank for qaurntine.