First off, Tropheus do not generally fair well as "pairs". You might want to start by reading this;
There seems to be a lot of confusion with regards to bloat, and how it can effect various species of cichlids. Hopefully the info below will help clarify some of the common misconceptions surrounding this condition. Protein Protein in & of itself does not cause bloat. Most...
www.monsterfishkeepers.com
I feed NLS AlgaeMax to my herbivores, as well as my non herbivores, but have seen many Tropheus breeding set ups in the past where regular NLS cichlid formula was fed exclusively.
AlgaeMAX pellet contains a diverse range of aquatic vegetation including a whopping 9 types of algae and seaweed.
•Ingredients. Algae; Chlorella, Ulva Seaweed, Red Seaweed, Kelp, Spirulina, Wakame Seaweed, Whole Antarctic Krill, Whole Fish, Eucheuma cottonii, Spinosum Seaweed, Chondrus crispus, Whole Wheat Flour, Omega-3 Fish Oil, Alfalfa, Astaxanthin, Capsanthin, Zeaxanthin, Vitamins, etc
•Analysis. 32% Protein. 5% Fat
Amazon.com : New Life Spectrum AlgaeMAX 2mm Enhanced Algae Pellet Pet Food, 125gm : Pet Supplies
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In nature, mbuna do not just eat algae, and they are not vegans.
In the wild, the cichlids found in the Rift Lakes have evolved & adapted to living in certain niches of the lake, which over time has forced them to become specialized feeders. (as per Ad Konings) Yet all of these specialized feeders will readily eat anything that's available. (as per Ad Konings) While a fish classified as a strict herbivore (such as a Tropheus moorii) may indeed spend its entire day scraping the aufwuchs, I can assure you that they would much rather eat a handful of worms if given the opportunity. In the wild they eat low quality foods because that's the only foods available, not because they choose to!
And while Tropheus and various Mbuna species may in fact be classified by the scientific community as strict herbivores, the reality is that even though algae dominates the stomach contents, the actual foods that make them grow are insect nymphs and larvae, crustaceans, snails, mites, micro-organisms, and zoo plankton, not vegetable matter. (as per Ad Konings)
Their long digestive tracts are designed as such so that in nature they can break down the complex plant matter that they consume, which doesn't mean that they can't properly assimilate more easily digestible forms of protein. Apparently this is a concept that some hobbyists fail to grasp.
Keep in mind that the vast majority of fish are opportunistic feeders, and are all omnivorous to a certain extent. Cichlids classified as carnivores don't just eat meat, any more than a herbivorous cichlid just consumes vegetable matter.
I prefer more nutrient dense pellets over flakes etc when feeding the vast majority of algivores, including mbuna, tropheus, etc that fall under this classification. When it comes to herbivores, especially algivores I also prefer to cover a wide variety of aquatic based plant matter in the food as in the wild most freshwater as well as marine species tend to seek out and consume very specific types of plant matter, be it diatoms (Tropheus brichardi) green algae such as Cladophora (Tropheus moorii), or the filamentous green algae Mougeotia preferred by adult O. lidole in Lake Malawi. The fish in the Rift Lakes are no different than various marine fish that for whatever reason (nutrient content or availability) consume specific algae, some preferring red algae over brown, or green.
IMO this is where NLS truly outcompetes all other herbivorous formulas, that typically use only kelp and/or spirulina in their food.
HTH