Ayo DJ Pauly up in the mix, here to answer your Q
Chocolate Zebras, scientifically known as Hypancistrus sp. (L-270) are primarily carnivorous. Most of what you feed them should consist of live or frozen foods. My advice would be to keep the remaining specimen fed on any of the available carnivore pellets (Hikari has a good carnivore tablet I believe, also various brands of shrimp pellets and such) and every now and then the feeding of say a decent spirulina pellet or I maybe I'm barking up the wrong tree. But something that can fill the nutritional gap, allowing them to receive the extra vitamins and such that are not present in the main diet, what i would do anyway.
Wouldn't be a silly idea trying to provide some enrichment also. Perhaps more caves, more cleaning to the tank, i'm unsure of how many water changes you do per week/month but Plecos in general are notorious for having a fairly high waste output, so if uneaten food and waste is accumulating on the bottom of the tank. Then i suggest making changes to the cleaning regime. Just for the well being of the fish anyway. I presume you're doing at least two water changes per week? With Juvi discus and all. Perhaps even move him/her to another tank. Plecos aren't too hard to look after, if you're interested you can PM me and i can provide some additional tips for you.
FNZAS, feel free to add on to what I've said , and perhaps correct me if I'm wrong , most of the Hypan info I get is from PlanetCatfish and such, so yeah
DJ PAULY OUT.