Remember to remove the false bottom during each cleaning. This will ensure that proper flow through to the drain is maintained When your screen is growing heavily, the algae strands will get long, and these strands will extend under the false bottom. When you remove the screen, strands can detach and will end up floating in the water in the bottom of the box. Use a soft-bristled brush to remove any algae from the bottom of the box. When I say "remove", it's really "snagging" the algae. If you can't easily access the inside of the box, place a small filter bag or filter sock over the drain before the start the flow back up after cleaning. After a few seconds, all the loose algae will be flushed out of the box.