The short answer for a cool-water school
White cloud mountain minnows are small, sparkling fish from cool mountain streams, and while a school can be kept in a 10-gallon tank, a 20-gallon long aquarium is the home that matches their energy. These minnows swim almost constantly, scattering across the tank, regrouping, and racing each other through gentle current, and that lifestyle needs length rather than depth. A long footprint also gives the water volume to stay cool and stable, which matters more for this species than for most tropical fish. Start with the long tank if you can; it is the single decision that shapes everything else about keeping them well.
Built for streams, not still corners
A white cloud's body and behaviour are stream equipment. It holds easily in moving water, feeds in the current, and uses eddies behind stones and plants to rest between runs. A home tank should echo that geography: a clear swimming lane along the length, rounded stones or wood creating slower pockets, and planting at the ends and back where fish can slip out of the flow. Unlike many small fish, white clouds are not hiding specialists; they are open-water fish that feel secure in a group in the open, provided the school is big enough. In a short tank the racing lane disappears, the school mills in a frustrated knot, and their colours and activity both flatten noticeably.
The unheated setup, done properly
White clouds thrive in cool water and usually need no heater in a normally heated home, which simplifies the equipment but not the planning. A room that bakes in summer sun can push a small tank too warm, so the bigger volume of a long 20-gallon, placed away from radiators and direct midday sun, is real protection. Moderate flow from the filter suits them, aimed along the tank's length so the school can ride it and rest behind decor. A secure lid is essential, because a startled school jumps together, and cool water holds oxygen well but a heavily stocked, warm spell can still stress them, so resist filling every spare inch with extra fish. Substrate and decor can stay simple: smooth gravel or sand, rounded stones, and hardy plants that enjoy the same cool conditions.
School size and signs the room is right
Eight white clouds is a good minimum school and a dozen in the long tank will scatter, regroup, and display in the way that makes them look like living sparks. Males show brighter fins and spar gently in the open when the group and the lane are right. Companions should share their cool, peaceful water; warm-water tropical fish are poor matches simply because the temperatures each side prefers pull the tank in opposite directions. A settled school uses the full length, feeds at all levels, and rests in the eddies at night. Fish gasping at the surface in a warm room, or a group that hangs in one corner avoiding the flow, are layout and temperature signals to act on promptly. Homes sharing minnow care can use KinsLe's Family Sharing so the unheated setup, school count, and seasonal temperature notes stay in one profile for every helper.