Not sure what else is in there but presupposing your water params are 'fine'; most importantly ammonia and nitrite, I'd check to make sure you're getting enough oxygen exchange in the tank. Those Bio's are a pain since unless you remove the canopy there are almost sealed and prone to possible low exchange rates. If you just added another/more fish, then more so.
You'd like a nice ripple on the surface.. even better w/ the top off (of the tank)
Water parms would be nice but with these symptoms I'd look to amm/trite and/or o2