A bumblebee goby is barely an inch of fish, black and gold banded, that spends its life perched on the bottom propped on its fins. Judged by body size it seems suited to the smallest tank on the shelf, but what it actually consumes is territory: each goby claims a small shelter and defends the patch around it, so the useful measure of its tank is floor area and hiding places, not gallons alone.
The practical sizes for a small group
A tank of about 10 gallons works for a modest group when it is laid out as a wide, low space with several caves, while 15 to 20 gallons is the comfortable choice for a larger group because the floor can hold a territory for every fish with room between them. Height contributes almost nothing; a tall column tank with a tiny footprint is worse for gobies than a shallow tank of half the volume. Keep the group either clearly several fish or be ready to watch one dominant individual claim the entire floor of a very small setup.
These gobies are most often kept in low-end brackish water, and the tank you choose must be one you are willing to maintain that way, with a lid, since they climb glass and explore filter intakes when given the chance.
Decor is the real space multiplier
In a goby tank, a cave is a room. Small ceramic tubes, halved shells, smooth stone stacks, and short pipe sections each become a claimed home, and the rule is one shelter per fish plus at least one spare, so a displaced goby always has somewhere to retreat instead of being chased across open sand. Break up sight lines between shelters with a stone or a sturdy plant, because a goby that cannot see its neighbour stops defending against it.
Use sand or smooth fine substrate they can perch and shuffle on, and scatter the shelters across the whole floor rather than clustering them in the prettiest corner. Plants that tolerate their water, such as Java fern attached to wood, add cover without taking floor space.
Feeding and behaviour in the space you give them
Territory is also about dinner. Gobies are slow, deliberate hunters of small meaty foods and poor competitors, so a layout with separated perches lets you deliver food near each fish instead of watching bold tankmates strip the water column first. In the right footprint you will see the behaviour the species is kept for: gobies perched in a row on their shelters, hopping between spots and flaring at neighbours in disputes that end in seconds because everyone has an exit.
Perching is the sign the footprint is working: a settled goby sits out in the open on its shelter, banded and upright, rather than wedging itself out of sight all day.
If squabbles in your tank do not end, if one fish lives permanently behind the filter, the floor is telling you it is full regardless of what the gallon count says. Add a cave before you add a fish, and never answer crowding by removing shelter. Noting the floor plan, shelter count, and group size in KinsLe Family Sharing keeps anyone rearranging the tank from consolidating the caves and collapsing every goby's territory at once.