The short answer for a tiny labyrinth fish
A sparkling gourami is a jewel of a fish, small enough to vanish behind a leaf, and a pair can live well in a 10-gallon tank. A small group is happier in 15 to 20 gallons, not because these fish swim far, but because each male needs his own planted corner and the group needs room to spread out when tempers rise. What counts as space here is structure: dense stems rising to the surface, floating leaves overhead, and still water between them. A bare tank of twice the size would feel exposed and hostile to a fish that spends its life threading through vegetation.
Life among the stems
Sparkling gouramis come from slow, heavily vegetated shallows, and their whole routine is built around plants. They pick tiny foods from leaves, rest tilted among stems, and breathe air at the surface through their labyrinth organ, so easy access to calm surface pockets is part of their living space. When breeding, a male builds a small bubble nest tucked under a floating leaf or among surface stems and guards it closely, driving away fish that blunder in, including other sparkling gouramis. Females need escape planting they can vanish into after spawning. Tanks that provide several separate thickets, each reaching the surface, let a group live as neighbours instead of rivals in a single shared bush.
Arranging a calm, covered tank
Pick a tank with a good footprint and fill it generously: fine-leaved stems at the back, bushy midground plants, and a raft of floating plants shading part of the surface while leaving some open pockets for breathing and nest building. Keep filtration gentle and shield any outflow, because current through the thickets exhausts these fish and tears nests apart. Warm, still air above the water suits their labyrinth breathing, so a snug lid that keeps the surface air humid is genuinely useful, not just jump insurance. Dimmer light under the floating cover encourages the shy, croaking displays these gouramis are loved for, and soft substrate planting gives fallen food and micro-life a place to gather where they forage.
Group size and the signs of enough room
A pair in 10 gallons, or two males with several females in a larger planted tank, are the groupings that most often stay peaceful; a lone male in a tiny thicket can also thrive. Add fish only when the planting is already grown in, because newcomers introduced to bare glass have no corners to claim and nowhere to hide. A settled group feeds throughout the thickets, males shimmer and croak from their own stations, and chases end in a few inches when the loser slips into cover. Relentless pursuit, a fish hiding at the surface behind the filter, or nests constantly destroyed all say the same thing: this group needs more planted separation, which may mean a bigger tank or simply more thickets in the one you have. For homes sharing gourami care, KinsLe's Family Sharing keeps each fish's corner, the planting plan, and breeding notes together in one place for the whole household.