BN's are the least picky eaters ever. dont think ive used a vegetable or fruit that they have turned their noses up, and im talking 5 or more different species. i've also had them feed on bloodworms and krill and a few other things. in the wild theyd eat insect larvae and fish eggs amoungst other things. royals arent that omnivorous and are similar to how herbivorous they both are. however both should have the nutrients found in meat, as both fish would graze on these foods too.
also ive never wasted my time buying any algae wafers (although have tried several different brands and types). i've always found that fresh fruit and veg to be a whole lot better, along with any algae growth in the tank (but that is a supplement not a base). cucumbers are good for roughage, which is needed by royals for their digestive tracts, but nutritionally isn't amazing. try things like shelled peas (very nutritious), potatoes, mangos etc. and milkman, they arent amazingly quick growing so dont expect a real monster too soon lol