Posted: Mon Nov 03, 2008 8:18 pm
Most likely it's a combination of dissolved debris and algae (to my knowledge beneficial bacteria is not visible). Don't know how large the tubing you're using is, but it is possible to clean it . The canister filter I have takes 5/8" tubing and to clean it I tied a brush to a piece of thin rope and pushed it through the tubing with a wooden dowel, then pulled the brush back through. A few times of doing this, then running some water through the tubing would clean it. The alternative is to let the gunk get to a point that the water rushing though the tubing will actually start pulling it off (I've done this as well).
Most tubing for canister and other filters is clear. The tubing for pond filters usually isn't.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-