I find a bit of algae can build up on the sides facing your filter. I usually use a tiny cup and scoop them up and put them in a jar. Then run the net under the tap with a bit of a scrub and then put them all back.
Someone taught me the best thing for cleaning it when you are finished with it. If you leave it to dry out completely THEN run water over it while scrubbing it against itself it comes out white again.
Uneaten food should be removed daily. To do that, use a nice piece of air line tubing as a siphon and just suck up the uneaten food. If you fail to properly maintain your fry habitat, you will lose many of the fry.