Mine are doing that too right now. It's a last ditch effort for them to survive. Just got this tank that was being neglected. Tested water and the Mg is >2000. Apparently stress and this value is causing it. Major water change tomorrow.
Not saying Mg is why yours is doing it. Just what I've found in my tank.
Not saying Mg is why yours is doing it. Just what I've found in my tank.