Hello everyone. I have a 35 gallon tank which has been set up for over a year. I have one goldfish and two algae eaters, no plants since the fish eat them. My question is why do I have so much brown gunk on the filter? I have to wash it every day or it gets clogged so the water goes over the overflow. The filter is for a forty gallon tank. I only feed the fish every other day and then only a small pinch of flakes, Any idea how to control the gunk and why there is so much of it? The tank sits in a corner away from any windows and had a light made for the tank that is on all day-off at night.