The bottom of the tank is a different climate
Your kuhli loaches spend their lives in the lowest few centimetres of water, threading through sand and leaf litter — and in a heatwave that layer is the first to fail. Warm water holds less oxygen overall, and the still water around the substrate, furthest from the surface where oxygen enters, runs thinnest of all. A kuhli's heatwave warning signs are easy to misread as charm: loaches draped over plant leaves halfway up the tank, hanging in the filter outflow, or out and restless in daylight are not being playful — they have climbed toward oxygen because the floor has run short. Normal kuhli behaviour in a heatwave looks like nothing at all: hidden by day, easing out at dusk to sift the sand.
Moving water where the loaches actually live
Surface ripple alone does not guarantee the bottom layer is served. Aim part of the filter outflow low, along the substrate, so a gentle current sweeps the floor without blasting it — kuhlis come from slow streams and hate a torrent, but they need the water down there replaced, not stagnant. An air stone buried near their favourite hide helps twice over, lifting oxygenated water through their shelter zone. Speaking of shelters: check where the caves, coconut halves, and dense plant thickets sit. A hide in a dead corner becomes a trap in hot weather, so nudge the most-used shelters into the flow's path. Keep the sand clean with light, frequent vacuuming — decaying matter in the substrate consumes oxygen exactly where your loaches breathe.
Cooling without frightening a shy fish
Kuhlis startle easily and are champion escape artists, so heatwave work on their tank should be calm and covered. Lower the light period — they prefer dimness anyway — and shade the tank from sun. A fan across the surface cools steadily; if you open the lid for it, replace it with a mesh cover, because a panicked kuhli can and will leave through a gap during a hot, restless night. Cool the tank with slow, small water changes of slightly cooler dechlorinated water added at the filter end. Never chase the number with ice against the glass near their hides; a cold patch on the floor sends loaches scattering, and the stress costs them more than a degree or two of warmth.
Feeding bottom-dwellers in hot water
Kuhlis eat at night, off the floor, and in a heatwave their dinner is an oxygen problem: a sinking pellet that lands at dusk and goes uneaten decays in the lowest-oxygen water in the tank. Feed after lights-out, in smaller amounts, where you can see the loaches gather, and lift out anything untouched by morning. Live or frozen foods fed sparingly are cleared faster than dry rations. If the loaches do not emerge to feed on a hot night, do not add extra 'in case' — an empty night harms them far less than a rotting one.
Keeping the checks visible at home
Because kuhlis hide, their care is easy to sign off without actually seeing a fish. Shared notes fix that: record where the loaches were last seen feeding, which shelters were moved into the flow, and the day's temperature, where anyone helping with the tank can read it. With KinsLe Family Sharing, relatives you pick can be given access to their profile, so a relative watching for loaches draped over plants can open that profile after dark.