The first pic is as close as I can truly get with it being shown. You can see it on the glass and on the circulation fan.Can u get closer pics? It could just be hydra.
I have a xl API canister filter right now on my tank. The tank is a 125 or 150 gallon. I have 2 circulation fans mounted on the left side to disperse the water from that side to the intake side. I am going to build a sump soon maybe.Can you describe your mechanical setup? It looks like it could just be a mechanical issue