Snails earn their place in an algae plan as grazers, not as a cure, and choosing between them comes down to how they graze and what happens to their numbers afterward. Two kinds cover many freshwater tanks well. The rest of the choice is about matching the snail to the surfaces you actually need cleaned, and being honest about the cause of the algae, which no snail can graze away.
Nerite Snails, the Steady Grazers
Nerite snails are the recommended first choice, and the reasoning is concrete. They graze steadily and patiently, working glass, wood, stone, and broad plant leaves in slow passes, and they keep at film and spot algae that many other grazers leave behind. Just as important for a keeper who wants control, they do not breed in fresh water: their eggs can appear as small pale dots on wood and glass, but those eggs do not hatch in a freshwater tank, so a keeper's chosen stocking level holds, month after month, with no youngsters appearing. A tank stocked with nerites this year holds the same crew next year, no population boom to rehome and no empty shells from a colony that crashed. Stock them for the grazing you need, roughly matched to the size of the tank and the amount of growth, and let them settle for a few weeks before judging, because a nerite's work shows as ground steadily held rather than a dramatic overnight clearing. Give an open-topped tank a lid or a lowered waterline, because a nerite following the film upward at night can wander over the rim and dry out on the floor by morning.
Mystery Snails, the Larger Scavengers
Mystery snails fill the other grazing role, bigger and more visible, cruising the glass and grazing soft growth and the film that forms on surfaces. They also scavenge leftover food and dead plant matter from the floor, which makes them useful in a tank where the algae problem rides along with general untidiness. Their appetite for some soft plants varies, so a planted tank keeper watches the first weeks and notes which leaves get attention. Mystery snails do lay eggs above the waterline in tidy clusters, which a keeper who wants no young simply removes, so their numbers stay manageable with a glance during the weekly glass clean. Between the two kinds, nerites are the patient surface crew and mystery snails the larger roaming cleaners, and many tanks run both without conflict.
The Honest Limit
Snails trim algae; they do not cure it. A snail grazes the growth that exists today, while the light and nutrient cause behind that growth keeps producing more tomorrow. Leave the lights running long hours over a rich tank and even a strong grazing crew only slows the film down. So pair the grazers with the actual fix: hours of light cut back to what the plants use, feeding measured so little reaches the floor, plant growth encouraged to take up nutrients, and glass and wood cleaned by hand during water changes so the snails start each week ahead rather than behind. Judge the plan over a month, by whether surfaces stay clear longer between cleans, not by whether a single snail is seen eating, because grazing is slow work done at snail pace across the whole tank.
In a shared household that month of judgment needs shared notes on the Family Sharing board: how many snails went in, when, and what the glass looked like each week. Noted on the Family Sharing board on KinsLe, algae trends become visible instead of argued about at the tank.