Set heavy decor so nothing can shift onto a sheltering fish: place rocks directly on the glass or on firm supports before sand goes around them, never balanced on sand that corydoras will dig away from underneath. When cleaning, hover the siphon just above the sand with your eyes on the shoal, check where every fish is sheltering before you move anything, and lift decor straight up instead of dragging it across the floor. Corydoras live their whole lives on the tank floor, snuffling through the substrate, sheltering under wood and rock, and resting exactly where your hands and equipment work during maintenance. Their risks during cleaning are physical: a shifted stone, a siphon tube, or decor moved carelessly across the sand.
Foundations: Rocks on Glass, Never Balanced on Sand
Build the hardscape from the glass upward. Place each heavy rock so its base sits directly on the tank floor or on a firm, flat support such as a buried slate or a plastic grid, then add or settle the sand around it afterward. A rock balanced on top of sand is a slow trap, since corydoras excavate the sand from beneath stones as they forage, and the stone eventually tilts, sinks or drops onto the fish sheltering in the hollow it created. Test every piece with a firm push before filling; decor that slides under hand pressure will move under fish pressure too. Stack nothing high and narrow, glue or pin stacked pieces where stacking is unavoidable, and leave a margin between heavy decor and the glass so a shifting piece cannot crack a pane or pin a fish against it. Choose smooth, fine, rounded sand rather than coarse or sharp gravel, since corydoras push their barbels through the substrate all day, and keep the layer shallow enough to clean without deep digging.
Vacuuming Without Harming the Shoal
Clean sand by hovering, not by plunging. Hold the siphon tube a finger's width above the surface and let the gentle draw lift loose debris while the sand itself stays put, moving slowly in overlapping passes. Corydoras do not always flee from a tube; a resting or sleeping fish can sit still until the siphon is nearly on top of it, and a startled fish may dart into the tube's path rather than away from it, so keep your eyes on the shoal the whole time and keep a thumb ready to pinch the hose or lift the tube away instantly. Work one section at a time, pause before moving to a new area, and count the group before and after cleaning so a missing fish is investigated immediately rather than at the next feed. Never chase debris into the corners where the group shelters, and accept a slightly untidy patch near their hiding place as the price of a calm tank. If a fish must be moved out for a deep clean, catch it into a container of tank water rather than netting it through the air, since corydoras have sharp fin spines that tangle painfully in mesh.
Moving Decor: Check, Lift, Never Drag
Treat every decor move as a fish count first and a rearrangement second. Before touching a cave, log or stone, watch the tank long enough to learn where each corydoras is sheltering, since at least one fish is usually tucked under the very piece you plan to move. Lift decor straight upward in one slow motion, hold it above its spot for a few seconds so any fish clinging beneath or startled from cover can drop clear, and set it down outside the tank or in a clear area rather than sliding it. Dragging is the dangerous habit: a stone dragged across the floor ploughs through the sand where bottom fish rest and can pin or crush a fish that does not move in time. Apply the same care in reverse when returning pieces, lowering them slowly onto glass or firm support rather than onto loose sand above a sheltering fish. With KinsLe, Family Sharing puts these corydoras precautions in front of every family member who shares the tank's care, rather than leaving them in one person's head.