so here's something new for everybody...
it's a very very simple setup, you don't have to clean it (maybe after 2 yrs), it's safe for fry and it's a great biological filter. we call it the hamburg filter.
you just get a filter mat (the blue stuff). it should be as big as your side glass, more or less. you can fix it to the aquarium glass so it makes a bow, a quarter-circle from, say, the rear glass to the side glass. it has to be 1" higher than the water level. it's important that it's tight, so that the water flows through it, and doesn't flow at the sides of it or over it.
behind this mat, you put a pump, which sucks the water to the space behind the mat. put a small tube hhhmmm at the pump's "exit" over the mat back into the aquarium and your filter is ready. that's all!
it's really cheap, easy to handle, and on top of it, you can plant it with java moss or something on the mat. behind the mat, you can put your heater. it won't look like a filter at all after some time!
there are more kinds of spaces you can build with the mat, e.g. rectangular, or you leave it flat and put an air pump behind it.... great for very small tanks.
NEVER had any problems with this. only to be cleaned when water level behind mat is lower than in front of the mat.
what'ya think??