I just skimmed over this post, so if I missed somethng or repeat something I aplogize.
Fishkeeping is not difficult, especially with CA cichlids. Herichthys do NOT consume fish in the wild in any significant amounts, perhaps a stray fry here or there. Just dump the idea of feeders altogether. They take in a huge amount of very low nutrition foods as part of their grazing in the detritus -- lots of plant matter and other fibers mixed with small amounts of tiny inverts and the like. Certainly not a high protein diet. You would have better results with an easily digestible staple food and much less meaty matter.
Modern pelleted foods are more nutritious and completely satisfactory for maintenance and conditioning of cichlids. Much of the belief that a variety is necessary comes from a time when pellets and flakes were made of cheap meals and fillers. Now, however, the better pellets are very high quality diets. It is unnecessary and actually diminishes results to feed a variety of foods, especially when those foods are not suitable for the species you're keeping (as in this case worms, crickets, etc.). Every breeder I know feeds a diet of or close to 100% pelleted foods. You can target certain veggie based formulas or just go with an extremely digestible staple pellet like NLS. You will likely get some resistance to this idea, but most of it is just regurgitated "common sense" from years gone by with no basis in science.
Pimafix and Melafix are crap, even though they are heavily marketed and seem to be widely used for....well......every-freakin-thing!. They are pointless and less effective than clean water and good food. More fish are killed with a shotgun medication approach than were ever saved.
Your fish DEFINITELY has an internal parasite. The only effective way to treat it is with medicated food. Get metronidazole by Seachem from your lfs, online, or just from a pharmacy. There are many online recipes that will tell you how to feed it, but basically just soak it into pellets. Treating the water with metro is almost useless for freshwater fish.
HTH!