This isn't miantence free, but it works. Take a Magnum HOB filter with the micron cartridge and stick a piece of 1/2" CPVC in the intake hole instead of the intake tube that it comes with. Stick an L on the end so that it touches the tank bottom. It will suck up the nasty stuff, but you'll have to change your cartriges pretty often. I learned this trick several years ago from DaveC.