The algae looks very yellow or is that due to the light? I think you can dial down the volume of air by 50%. You just want enough to break the surface tension to keep the water from getting stale but also not cause a lot of water movement inside. I know in the wild, they deal with ocean waves but keeping it calm should help them feed easier.
I'd get rid of the egg crate, they could get stuck in it. They're not the greatest of swimmers that I've seen, they are lazy eaters. If anything just pick the least porous looking rocks.