A mystery snail will graze algae and biofilm all day, which tempts many keepers to feed it nothing at all, but a tank rarely grows enough of the right food to sustain a large, fast-growing snail on its own. A healthy mystery snail diet deliberately adds plant-based sinking foods, fresh vegetables, calcium for that big spiralled shell, and a little protein, so both the soft body and the shell it carries stay strong.
Start with grazing foods that sink
Use an algae wafer, spirulina-based pellet, or other sinking plant food as the regular base, dropped where the snail can find it on the glass or substrate. Mystery snails feed with a rasping mouthpart that scrapes surfaces, so foods that hold together while they graze suit them better than fine powders that cloud the water. Feed in the evening if quicker fish steal daytime wafers, and size the portion to the number of snails rather than offering a full wafer to a single animal in a small tank.
Blanch vegetables for real meals
Fresh vegetables turn grazing into proper nutrition. Blanched zucchini rounds, spinach, kale, and green beans, softened briefly in hot water and cooled, are readily eaten and easy to weight down with a vegetable clip or a clean fork. Leave a piece in for most of a day, then remove what remains before it breaks down and dulls the water. Rotating two or three vegetables across the week gives a broader mix of minerals and fibre than living on one favourite, and watching which vegetables disappear fastest tells you what your individual snail prefers.
Protect the shell with calcium
That smooth, unbroken shell is built from calcium, and a snail short of it develops pitting, thin edges, and a fragile new growth line. Calcium can come from calcium-rich vegetables, a plain cuttlebone piece resting in the tank, crushed coral in the filter where a keeper already uses it, and water that is not extremely soft and acidic. Check the shell weekly in good light: new growth at the opening should look even and solid, not papery or eroded. A snail retreating for long stretches with a deteriorating shell deserves prompt attention to water and diet, and a specialist aquatic vet's advice if the damage is spreading.
Add a little protein, and watch the leftovers
Mystery snails are not strict herbivores, and an occasional protein-containing sinking pellet or a few thawed bloodworms that reach the floor supports body condition, especially in breeding females producing clutches. Balance is the point: heavy protein feeding fouls water quickly and encourages the snail to ignore its plant foods. Whatever you offer, lift out uneaten soft food promptly and keep ammonia-producing waste low, because a snail lives in constant contact with the water its food decays into.
Recording the vegetables your snail favours, its calcium source, and any shell changes in KinsLe Pet Passport keeps that whole feeding picture together in one packet a vet or sitter can read in seconds.