For one bristlenose pleco, a meal is about one algae wafer, or a thick slice of blanched zucchini or courgette on the days you offer vegetables instead. Drop it in as the lights go down, because bristlenoses feed most confidently in the dim hours, and put it near the pleco's usual cave or wood so it finds the meal before the other fish do. A healthy adult does well on that deliberate meal most evenings; a fast-growing juvenile should rarely miss one.
Grazing is a supplement, not the meal
The commonest bristlenose mistake is assuming the algae in the tank feeds the fish. A bristlenose rasps algae and biofilm all day, but a reasonably clean aquarium simply does not grow enough to sustain one, and the fish quietly loses condition while the glass stays spotless. The wafer or vegetable portion is the actual diet; the grazing is grazing. You can judge the balance by the fish itself — a well-fed bristlenose has a flat to slightly rounded belly, while a sunken, concave underside means the deliberate meals need to get bigger or more frequent.
The driftwood is part of the dinner
Bristlenoses rasp wood fiber as part of normal digestion, so a piece of driftwood in the tank is feeding equipment, not decoration. Position the evening wafer near that wood and the pleco will work both through the night. If your pleco has no wood, add a piece before you go increasing food amounts — a fish that cannot graze fiber between meals often looks hungrier than it is, and piling in wafers to compensate just fouls the water it lives in.
Vegetables: how much and how long
Blanch zucchini, cucumber, or a shelled pea briefly so it sinks and softens, fix it under a clip or fork on the substrate, and treat one generous slice as the meal in place of a wafer, not as well as. Soft vegetables collapse quickly in warm water, so anything left in the morning comes out — a pleco that wanted it would have finished it overnight. Rotate the offerings across the week: wafer most evenings, vegetable twice or so, and the fish gets the variety its plant-heavy gut is built for.
Sharing the bottom with other fish
In a community tank the question is less how much you drop in and more how much the pleco actually receives. Fast mid-water fish will mob a wafer dropped in daylight; evening feeding, a spot near the pleco's hide, and occasionally two half-wafers at opposite ends of the tank solve most of the theft. If morning leftovers keep appearing, the meal is beating the fish — cut the wafer before you cut the frequency, and see an aquatic vet if a pleco with a good appetite develops a swollen belly or stops producing the usual long waste strands.
Evening feeds are the easiest for a household to duplicate by accident, since everyone passes the tank after dinner — logging the wafer or vegetable in KinsLe's Care Teams, marked complete once it goes in, keeps your bristlenose on one meal a night.