Build the quarantine around a fish that burrows and hides
A kuhli loach experiences the world through its barbels and its belly, and a quarantine tank should be furnished accordingly. Cover the bottom with soft sand it can sift and half-bury in, or leave smooth bare glass; sharp gravel is the one real mistake, since it scrapes a scaleless belly raw. Pile in hiding architecture: short lengths of pipe, a coconut cave, leaf litter or a dense plant thicket, arranged so a loach can travel the whole tank without crossing open ground. Fit the lid perfectly and block the filter intake with sponge. Kuhlis escape through gaps that seem physically impossible, and a loach dried on the floor is the commonest quarantine tragedy with this species.
Why being scaleless changes the health picture
Kuhlis wear no armor of scales, and that shapes quarantine in two ways. First, parasites and irritants reach their skin more easily, so wild-caught loaches, which most shop kuhlis are, deserve real watching for the scratching against objects and fine white dusting that announce skin trouble. Second, many standard fish treatments are harsh on scaleless species, which is exactly why catching a problem by observation matters more than treating on suspicion: if treatment ever is needed, it must be chosen with scaleless fish in mind and watched closely. Quarantine is also where a loach underfed at the shop can be fed back to a plump, rounded body without competition, since a sunken kuhli belly tells of a fish that needs groceries before it needs anything else.
Observing a fish you mostly see at night
You will learn almost nothing about a kuhli at midday, so schedule your watching for the hour after lights-out, when the group emerges to forage. Healthy kuhlis snake through the plants in loose company, drape themselves over leaves like dropped ribbons, and fall on sinking food with real enthusiasm. Drop a small sinking pellet or a fragment of wafer after dark and confirm that every loach finds food; a fish that stays buried and never emerges across several nights is the one to worry about. Also note group numbers: kuhlis kept in a proper group are bolder and feed better, so quarantine at least the group you intend to keep rather than a pair.
Keep the water boringly stable
Loaches in quarantine need nothing exotic, just steadiness: warm water in the mid-to-upper seventies Fahrenheit, a cycled gentle filter, and small regular water changes so quality never slides while they are under observation. Because they are sensitive fish, avoid sudden changes of any kind, big water swaps, temperature lurches or bright light dumped on a dark tank. If you run more than one tank, use separate equipment on the quarantine or work on it last, and let nets dry between uses, since a scaleless fish is the last one you want meeting anything carried from another setup.
Graduation day for loaches
After a few weeks of nightly activity, good feeding and a body that has filled out, the group is ready. Acclimate them slowly to the main tank's water, release them near cover in the evening, and do not panic when they vanish entirely for the first days; that is normal kuhli behavior in a new landscape. Keep the nightly check going once they graduate by putting it on the household rota in KinsLe Care Teams, with the evening feeder logging appetite and activity each night, so the fish you can only judge after dark still get judged every day.