The Community Tank is Having Trouble.
Drop the water level 50%.
Pull your sponge filters and wring them out in the *fish tank water* not under the tap.
Refill the tank to 90%.
Apply at least a teaspoon of baking soda.
Go out to your pond, pull out some sponge material from the filter, and wring it into a bucket. Get a lot. if it is a dark, greenish-brown, then you win.
Slowly put at least a quart (but preferably a half gallon) of greenish squeezins into the tank.
⭐️ It is better for the fish if you put the squeezins in a container with a small hole punched in it. And let it trickle into the system, instead of flooding it.
Let your ‘wrung-clean’ filters pick up the bio-active ‘goo’.
In the morning, add another teaspoon or two of baking soda.