I have now moved on to a species tank for my Mbuna but several years ago, when new to the hobby, I kept them in several community tanks.
I had the best luck with barbs. I had a 55 gal tank for a couple years with a 3-4 Mbuna mixed with a school of Tiger Barbs and Golden Barbs.
Silver Dollars worked well. No trouble with Clown Loaches.
I now keep the water in my species tank alkaline with crushed coral, but earlier I always gave up on keeping the water hard. The Mbunas seemed healthy and fine swimming in my tapwater. The Barbs seemed to be equally able to cope with the harder African water.