Tropheus are, for the most part, herbivores, and specifically algae
grazers, which have a very long digestive tract, and need to be fed often, with
the correct diet. 
Many foods that are good for most Cichlids can be harmful
(over the long term) to Tropheus.
Tropheus are notorious for "bloat", an intestinal disorder that can
be triggered by diets heavy in animal proteins. To minimize this, feed primarily
algae based foods such as a good spirulina flake. During their algae grazing,
they also ingest small crustaceans and other microorganisms, so a bit of protein
is acceptable.You can feed a higher protein flake now & then, like Brine Shrimp
flake or freeze dried Krill, but it shouldn't make up the majority of it's diet.
Try to feed often, I recommend 3x daily, or more if you can, but feed sparingly,
about all they can consume in 3 minutes.
It's also a good idea to provide alot of light to encourage algae growth on
the rockwork, your Tropheus will graze constantly, and it's quite a sight!
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