Ask the question in gallons and the answer is five — cherry shrimp are tiny, produce almost no waste, and a colony of dozens fits a small tank physically. But shrimp do not die of crowding; they die of change. Temperature, hardness and chemistry all move twice as fast in five gallons as in ten, and that is why ten gallons is the minimum worth recommending to a first-time keeper who wants a colony that quietly multiplies instead of repeatedly crashing.
Stability is the real requirement
Cherry shrimp are the hardiest of the dwarf shrimp, tolerating a broad band of conditions — but they need those conditions to stay put. A cold night, a large water change with mismatched water, or a trace of copper from a medication can ripple through five gallons before you notice, while ten gallons absorbs the same event. Whatever size you choose, age the tank first: a month or more of running with plants builds the biofilm that is a shrimp colony's main food, and a brand-new sterile tank starves shrimp that technically fit in it.
Stocking the colony
Begin with around ten shrimp of mixed sexes — the deep red ones are females, the paler ones mostly male — from a single source, so their water preferences match your tank's habits. In a stable ten-gallon with moss, fine-leaved plants and leaf litter, those ten become a hundred without any intervention beyond steady water and light feeding. Population self-regulates against food: if the colony plateaus, it is grazing-limited, not space-limited, at these sizes.
The filter intake problem
The one piece of equipment that decides success in small shrimp tanks is the intake. Any filter strong enough for the tank will draw in baby shrimp, which are near-invisible for their first weeks. A sponge pre-filter over the intake, or a sponge filter outright, designs that loss out — and the sponge becomes a favourite grazing surface in its own right. Hang-on filters are fine with the sponge fitted; check it weekly, because a clogged pre-filter quietly slows the whole filter.
Fish, or no fish
Ten gallons with fish is a different colony from ten gallons without. Small fish — even rasboras and guppies — snack on baby shrimp, so a mixed tank produces a shy, slow-growing colony that hides in the moss. Shrimp-only, or shrimp with snails, is where the confident, everywhere-at-once colony behaviour comes from. If you want both fish and a booming colony eventually, run the shrimp tank a few months first so numbers and hiding cover build up before any fish arrives.
Judge the colony by coverage, not counting
You will never census a shrimp colony exactly — they moult, hide, and the young are specks — so judge the tank by grazing coverage instead: moss combed clean, a steady scatter of shrimp visible at any glance, and females carrying saddles or berries much of the time. In a healthy ten-gallon those signs show within a couple of months of the founding group. If the visible count collapses suddenly, test the water before blaming predators: in a shrimp-only tank a chemistry swing is almost always the culprit, and the small volume that makes these tanks charming makes their water unforgiving.
The colony's care is a rhythm of small tasks — weekly partial changes with matched water, sponge squeezes, sparing feeds — and KinsLe Care Teams lets you assign those named jobs around the household, each ticked off with a timestamp so the little tank never gets two big changes in one week.