Six or more, in water that stays cool
White cloud mountain minnows come from the cool, flowing streams of their namesake mountain in southern China, and both halves of that origin shape the answer. They are schooling fish that need six companions at minimum — eight to ten for the full display of flared fins and sparring males — and they are temperate fish that live longest in unheated water, roughly the low sixties to low seventies, rather than in a tropical tank. A group fits a ten-gallon tank, though twenty gallons of length flatters their streamlining and gives the school room to run.
That temperature preference is the grouping decision most often missed. A perfect school of ten still fades early if it spends its life at tropical temperatures, which shorten white clouds' lifespan and dull the red in their fins.
Behaviour of a white cloud school
Males are the showmen: slimmer, brighter, and constantly unrolling their red-edged fins at rivals in displays that resolve without damage. The group holds in midwater over the current, scattering for food and reforming in the flow. In cool, oxygen-rich water with a gentle current to swim against, a school stays active all day; in warm, still water it goes quiet and listless, which owners misread as the species being dull.
They are peaceful to the point of vulnerability, outcompeted at feeding by boisterous fish, so the school should be the tank's pace-setter or share with equally gentle temperate companions.
Building the stream tank
Fine gravel, smooth stones, and plants that tolerate cool water — many common stems and mosses do — recreate the stream edge. A filter outflow arranged to give one lane of real current lets the fish choose between exercise and rest, and they will visibly commute between the two. Tank mates from the same thermal world include danios, rosy barbs, and certain small loaches; shrimp colonies also thrive at these temperatures.
White clouds are undemanding about chemistry within a broad neutral range, and their hardiness about water, paired with their strictness about temperature, is the species in one sentence.
White clouds also make an unusually honest indicator school for the whole temperate tank. Because they are active, visible and quick to change behaviour, a group that suddenly hugs the bottom or stops displaying is often the first sign that a filter has failed or a heatwave has pushed the room's water warmer than their comfort allows. Keepers who watch the minnows daily catch equipment problems a day earlier than those who only test water on schedule, which is a practical argument for a visible school of eight over a token trio.
Keeping the school complete and compatible
Because they are inexpensive, white clouds are often bought as an afterthought and their numbers left to drift. Count them monthly — a school that falls to three stops displaying and starts hiding — and top up in fours so newcomers arrive as their own subgroup. Note the tank's unheated status and temperature range in the shared notes, because the most damaging addition to a white cloud tank is a well-meant tropical fish bought by someone who did not know. KinsLe Family Sharing keeps the school count and the cool-water rule attached to the minnows' profile, in front of every household member before the next purchase is made.