I have a large plastic storage container for which I made a cover out of cheap wood furring strips and plastic screen. If I cant get daphnia started, I leave the cover off and get the mosquitos started. Once I have larvae, I put the cover on to prevent escapees. If I see adults hanging on the screen, I hit it with a hose sprayer before I take the cover off. That usually takes care of the few winged adults that appear. If you use a large mesh net, you will get the larger larvae and the small ones will slip through to grow a little more. you can always use a brine shrimp net if you want small ones to feed fry. Be sure to dechlorinate your water if using tap water. If you use up all of the larvae, just leave the cover off for a few days until you get more larvae. Most fish love mossies, and some, like bettas and killies, have evolved to eat them with their up turned mouths.