Sand changes the cleaning method in a corydoras tank, because dropped food and waste do not vanish down into the grains the way they do in gravel. Everything rests on the surface in plain view, which looks untidy sooner, yet it also means a well-judged clean never needs to disturb the bed itself — important in a tank where the fish spend their days resting on, sifting and sleeping against that sand.
Why waste stays on top
Fine sand packs too tightly for debris to work its way down, so pellets that missed the school, fragments of wafer and ordinary mulm all settle as a visible layer. Corydoras make the picture messier and cleaner at once: their constant snuffling stirs the surface and keeps waste from lodging in dead spots, but it also spreads a fine film across open areas. Because the layer sits on top, removing it is a surface job. Digging the tube into the bed only buries debris deeper, clouds the water and can compact patches of sand where trapped waste then decays out of sight.
The hover-and-swirl pass
Start the siphon, then hold its wide end roughly a finger's width above the sand and move slowly. Waste is lighter than sand grains, so the upward pull takes the debris long before it takes the bed. Just before each pass, circle the tube tip gently a centimetre or so over the surface: the small swirl lifts mulm off the grains, and the siphon catches it mid-rise instead of chasing it across the tank. Work one section at a time — behind the wood, along the back glass, under the plant edges where flow drops — and pause between sections so drifting particles settle or reach the tube rather than resettling elsewhere.
Working around corydoras and fry
Corydoras are curious rather than fearful, and youngsters will drift toward the disturbance to investigate whatever the swirl has uncovered. Keep a thumb ready over the tube outlet so you can break the suction instantly if a small fish approaches the intake, and fit a piece of fine mesh or stocking over the end on a fry tank. Move the tube away from resting fish instead of expecting them to move for you. Before the bucket is emptied, swirl it, let it settle and look carefully: a stray fry against the pale bucket base is easy to miss and simple to net straight back.
How much sand loss is normal
A spoonful of grains in the bucket after a full clean is normal and nothing to chase; rinse it and tip it back, or top up the bed occasionally. Losing noticeably more means the tube is riding too low or the siphon is too strong for fine sand — raise the tube, kink the hose slightly to slow the pull, or switch to a narrower tube for detail work around decor. If one corner always collects the heaviest layer, that is the tank's flow pattern speaking, and giving that corner an extra pass each week keeps the whole bed looking even.
Keeping the weekly clean shared
This is a small job that suffers when it depends on memory: skipped twice, the surface film builds up and the next clean turns into a long excavation. Put the Saturday hover-clean on Care Teams in KinsLe, and the helper's finished pass is recorded with its completion time for everyone to see.