IMO, Aggressive Botia loaches make very good scavengers in an African Cichlid tank. Any of the Tigers - Syncrossus
Berdmorei, Hymenophysa & Helodes (particularly aggressive). YoYo's would probably do well.
I keep, four Red Tails Loaches (Y. Modesta) & a solo Berdmorei Tiger in my African cichlid community.
The noted loaches are very durable, efficient scavengers, but need a well constructed hardscape to survive.
Some successfully keep Clown Loaches with African Cichlids. IMO they are a little too shy & fragile. Loaches won't graze on algae. Your mbuna should be grazing on algae, but not to the point that manuel cleaning will be eliminated.
Your tank is pretty much maxed out. The Venustus will likely eventually out grow the tank. If your fish are still juveniles, look into getting a few Rusty Cichlids, a relatively peaceful Mbuna & a Steveni Tiawan Reef Hap. A smaller algae grazing Hap. The males are very colorful.