Night behaviour tells you a young kuhli is ready
A young kuhli loach is ready for the main tank when it runs a confident night routine: emerging after lights-out, weaving through cover with that eel-like swimming motion, sifting the surface of the substrate, and retreating smoothly into shelter at dawn. Kuhli loaches are nocturnal bottom-dwellers, so daytime stillness in a youngster is normal and tells you little. Judge readiness after dark with a dim light instead. A young kuhli loach that feeds eagerly at night, keeps clear brown-and-cream banding, and has a gently rounded underside is growing well. One that stays buried for nights on end and looks thin when it finally appears is not ready to compete in a busier main tank, even if its length seems adequate.
Tankmates, not adult kuhlis, set the size limit
Adult kuhli loaches welcome youngsters and often pile together in the same hide, so predation risk comes entirely from the main tank's other fish. A slender young kuhli loach looks remarkably like a worm or small snack to a large cichlid, big gourami, or sizeable catfish, so youngsters should only move when their girth puts them clearly beyond an easy mouthful for the largest resident. In a gentle community of small fish, young kuhli loaches can move much sooner. Also consider boisterous bottom-dwellers: pushy loaches or large Corydoras groups will not harm a young kuhli directly, but constant disturbance at floor level can keep a shy youngster from feeding, which shows up as slow growth rather than injury.
The main tank floor must be ready before the move
Prepare the main tank for young kuhli loaches before acclimation begins: soft sand or very smooth fine substrate they can push through without scraping their scaleless skin, plus dense floor-level cover from leaf litter, coconut caves, driftwood tangles, or thick plant bases. A tight lid is non-negotiable, because kuhli loaches of every age explore upward along glass and cables and can escape through surprisingly small gaps, and a youngster is thin enough to use gaps an adult cannot. Check filter intakes for openings a young kuhli could enter while seeking a dark tube to hide in, and cover them with fine sponge. Release youngsters directly beside cover after dark so their first act in the new tank is finding a proper hide.
Confirming young kuhlis have settled when you rarely see them
Settling checks for young kuhli loaches happen at night: a settled youngster appears at evening feeding, takes sinking foods and frozen morsels from the floor, and grows steadily between sightings. Because these fish can hide for days, use feeding response rather than daily headcounts — lay a small food portion near their hide after lights-out and watch whether the youngsters emerge for it. A young kuhli loach seen in daylight sitting exposed, breathing fast, or with faded, patchy bands should be caught gently and checked in a quiet tank. Note each youngster's chosen hide and night-feeding response in KinsLe through Care Teams so a sitter or family member does not dismantle the youngsters' shelter during a routine weekend clean.