I wondered if there was sexual diamorphism in shrimp and that might be the case. The volcano was to complete the tank theme of underwater volcanoes.Larger means likely all females, which might explain the lack of babies. Common names are hard--red crystal is used for a couple different animals.
I probably wouldn't add the bubbler. There's no real reason, and it will disturb the surface enough that it might prevent the gouramies from breeding again--they're bubble nesters, and usually build at or near the surface.
