what fish best for substance cleaning

What's a good equivalent of a corys and clowns for keeping the
substance fairly clean.

I used to have a couple of clowns, flying fox and an algae eater in my
main cichlid tank but they were clearly  not enjoying the high ph so I
have moved them out (not so sure the algae eater was so affected but
the others definitely were).

However, the substance has already begun to get dirty (I use coral
sand on top of normal sand) and I would like to find something
suitable to put back in to help clean it up.

My ph is 8.2 in a malawi tank made up of mbuna


Cheers


Brian