Just a confirmation re beef heart. Dr. Stephan Tanner does presentations at events and last March I attended one he did on Pleco of the Rio Xingu (I keep and breed a few such species). As part of his presentation he dealt with fish and diet. One thing he stressed, and which I have always believed, was not to feed beef heart to any fish. Not all concur with this opinion.
However, vegetarian fish should rarely be fed meaty foods and never as often as you are doing. I suggest you research Malawi Bloat. I will start you off with the following information from cichlid-forum.com:
Three Main Causes For Bloat
3.) Improper diet. Many cichlids - particularly herbivorous ones - have long intestinal tracts, requiring a relativley longer period of time to digest their food. Consequently, it is quite common for these cichlids to develop intestinal problems. The decomposition of improperly digested, or improperly excreted foods can irritate the intestinal wall, and stress the fish, giving the invasive parasite a foothold. This can often come about when a primarily herbivorous, algae-scraping cichlid (like Tropheus or Pseudotropheus spp.) is fed high protein foods such as bloodworms, or pellet and flake foods containing large quantities of fish meal. Slimy or soft foods, such as brine shrimp, should be avoided and replaced with crunchier foods such as mysis. In light of this information, and experience, it is important to avoid certain foods, and to go light on others. (For a detailed discussion of this topic, see Feeding African Cichlids.)
The Feeding African Cichlids info mentioned above states:
Many Cichlid foods are good and appropriate for all cichlids, be they carnivorous or herbivorous. What you want to watch out for are foods high in fat. You especially want to avoid anything that has beef heart or products from other warm-blooded animals