I got a problem and cannot find the cause. Maybe someone can think what is causing this.
I'm using a Fluval 406. I am getting air into the canister and it is causing (1)loss of flow, (2) impeller rattle, and (3) air in the out-flow when I get it flowing again.
I have no water leaking from the canister. I have checked all hoses to see if any are sucking in air. I did have the hoses long but I shortened them so is straight from the tank to the in-flow and the out-flow. Everything is perfect except for the air pockets.
You can try putting a silicone grease on the seals or replacing the seals (generally a good idea every few years). Look up your specific filter and make sure you have all the parts and they are in the right place. A small hole or gap anywhere can cause air to suck in without leaking water out.