Work out which kind of loach you are actually shopping for
There are three distinct groups here. Social bottom loaches — clown and yoyo — are boisterous, long-lived botiids that want a real group, a big footprint and warm, well-filtered water. The hillstream loach is a specialist: cool, fast, oxygen-saturated water and a diet of biofilm scraped off hard surfaces. Nano loaches — dwarf chain and rosy — stay small enough for planted tanks under 100 L and behave more like tiny schooling fish than substrate lurkers. Kuhli and weather loaches sit off to the side as the burrower and the cold-tolerant oddball. Decide which of those tanks you have before you decide which fish you like.
Group size is not optional for any of them
Every loach on this list is social, and the minimums in our database are honest minimums, not suggestions. Kuhli, dwarf chain and rosy loaches want six or more; clown and yoyo loaches want five or more; hillstreams and weather loaches want three or more. A single kuhli hides permanently and you never see it. A single clown loach becomes withdrawn and often stops eating properly. Under-grouped botiids also redirect their energy at tank mates — most "my yoyo loach turned aggressive" reports are a group-of-two problem, not a species problem.
Flow and temperature split this list in half
Clown, yoyo, kuhli and dwarf chain loaches are warm-water fish (24–30 °C) that want moderate flow. Hillstream loaches want 18–24 °C with turnover high enough to ripple the surface and a powerhead aimed along the glass — they will not tolerate a warm, still tank, and pairing them with discus or dwarf chain loaches is a slow failure. Weather loaches sit at 15–25 °C and are genuinely happy unheated in a cool room. Rosy loaches prefer the low end of tropical at 20–26 °C. Check your existing tank temperature before you shortlist anything.
The hillstream needs a purpose-built tank, not a corner of yours
Sewellia lineolata evolved on rock faces in fast Vietnamese streams. It needs a mature tank with algae and biofilm already established on smooth stones and glass, strong linear flow from a powerhead or spray bar, high dissolved oxygen, and cool temperatures. Bare new tanks starve them; warm tanks suffocate them. If you can commit to that setup, they are one of the most rewarding fish in the hobby — flattened, patterned, and constantly grazing in the open where you can see them. If you cannot, pick a different loach.
Sand, hiding places, and a lid
Loaches probe substrate with sensitive barbels, so sharp gravel wears them down — sand or smooth rounded gravel is the default for kuhli, weather, clown and yoyo loaches. All of them want caves, driftwood tangles and shaded overhangs, and they will use every one of them. Kuhli and weather loaches in particular are escape artists that will find any unsealed filter cut-out or gap at the back of the lid. Seal the gaps before you add the fish, not after you find one on the floor.
Snail control is a side effect, not a job description
Yoyo and dwarf chain loaches will strip a pest snail population fast, and that is a legitimate reason to like them. It is not a reason to buy them for a tank that is too small or too cold. A yoyo loach needs 150 L and a group of five whether or not you have snails, and it will also harass nerites and small shrimp once the pest snails are gone. Buy the loach because you want the loach.
