airstones are fine for smaller tanks. larger tanks you what the setup thath causes waves, for lack of correct terminology. Agitates water and provides oxygen more effciently than bubbles. The point at which that becomes true? 50g? probably need an aquarium knowledgebase.
the build up would be impossible to avoid in the mats. (someone mentioned they had personal use ,here. said they clogged, but read this elsewhere too.)