x2 on the clown loaches maybe a decent royal pleco mine stays near the bottom or a small cat of some kind
+1 on the synodontis they work perfectly with your malawi cichlids as they live togteher in the wild.
As for the fish you already have; Yellow labs are great, you will not have any problems with them at all, get a few more and they will do well. The bumble bee can be a bit of a pain in the bum literally as the are typically more aggressive, so I would stick with only the one. Also the Johanni can be a bit of a head banger again stick with one. If you want to add some more colour look at some Metriaclima Estherae, they are popular easy to fins and similar in aggression level to your labs. They also come in a great range of colours from pink, red, pearl and blue. so perfect for a kids room.
The livingstonii (giraffe colour) will get quite big at 10" and may be a bit big for your tank, where as the other fish you have will all only reach 4"-6".
One other thing to mention is the lab, bumble bee and johanni are all algae grazers so feed a good quality vegetarian diet, spirulina flake is perfect. They dont do well on high protein foods like blood worm, brine shrimp and these should be avoided.
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