Why blanching makes vegetables edible for grazers
A raw zucchini round might as well be a pebble to a small pleco. Algae eaters feed with rasping mouthparts built for scraping thin films of algae and soft plant tissue off surfaces, and the crisp cell walls of uncooked vegetables resist that scraping for hours. Blanching — a brief dip in simmering water — breaks those cell walls down just enough that a common pleco, a school of otocinclus or a mystery snail can tear mouthfuls away. It also drives air out of the tissue, so a spinach leaf or cucumber slice sinks to the grazing surfaces instead of bobbing at the top where bottom feeders never look. The vegetables your algae eaters will use best are zucchini, cucumber, spinach, kale, sweet potato and shelled peas; harder roots need the longer end of the blanch, tender leaves only a few seconds.
The blanching routine, vegetable by vegetable
Wash everything first, because market vegetables can carry residues you do not want in a closed tank. Slice zucchini and cucumber into rounds about as thick as a coin, cut sweet potato thinner so the heat reaches the middle, and leave spinach and kale as whole leaves with the toughest stems trimmed away. Bring a small pan of water to a simmer, lower the pieces in, and watch for the change rather than the clock: rounds are ready when they turn slightly translucent and bend without snapping, usually after a minute or two, while leaves are ready the moment they wilt and darken, in well under a minute. Lift the pieces out and drop them into cold water to stop the cooking — vegetables that go mushy in the pan will fall apart in the tank and foul it. Pat them dry-ish, and they are ready to serve or to freeze flat in a bag for later veggie nights.
Serving it where the grazers actually feed
Anchor the food at the bottom, because a floating slice feeds nobody in this tank. A stainless vegetable clip suctioned to the glass at substrate level works well, as does spearing a zucchini round on a clean stainless fork laid on the gravel; never use anything that can rust or flake. Place the food near the pleco's usual hide or along the glass and wood where otos already graze, so shy fish find it without crossing open water. Offer vegetables in the evening if your algae eaters include a nocturnal pleco, since he will rasp through the night while the lights are off and the bolder fish are resting. One round or a couple of leaves is a serving for a typical community of grazers — this is a supplement alongside their algae and staple foods, not a replacement for either.
Timing, leftovers and water quality
Softened vegetables have a short tank life. Within about a day they begin to break down, and a slice left for two days will cloud the water, feed a bacterial bloom and push ammonia up in a small tank. Lift out whatever remains at the next morning's check and note which vegetables were finished and which were ignored — plecos that ignore cucumber often demolish sweet potato, and otos may only take the softest leaves. Rotate two or three vegetables across the week so the grazers get a spread of nutrients rather than one food repeated. If the water clouds after a veggie night, the serving was too big or stayed too long; halve it next time. Recording those rotations in KinsLe's Care Teams turns veggie nights into a standing duty with the day's vegetable named, so the person feeding knows what to blanch and the leftovers check never gets skipped.