An uncovered filter intake is a quiet hazard in a guppy tank. The slots or holes that draw water in also draw anything light, weak, or curious that drifts close, and a guppy fry is all three during its early days. Adults in good health can usually pull away from a gentle intake, yet a sleeping fish, a tired fish after breeding, or a fish weakened by age can get pinned against the slots and injured before anyone notices. The answer is mechanical and simple: cover the intake with a guard that spreads the draw across a wide surface, keep the guard clean so filtration keeps working, and check the whole setup on a weekly rhythm.
Fit a cover that spreads the draw
Fit a sponge pre-filter over the intake tube, pushing the sponge fully onto the tube so no gap remains at the top where a fry could slip behind the cover. A fine mesh sleeve tied or fitted snugly over the intake slots works where a sponge will not fit, provided the mesh stays taut and the edges cannot flap loose in the current. Confirm after fitting that water still flows from the filter return at a rate close to the usual rate, because a cover fitted over a dirty intake can reduce flow from the first hour. Run the filter and watch for several minutes: fry should be able to swim near the cover, touch it, and swim away without effort. A cover that still pins a curious fry is either too coarse, too tight against the slots, or carrying debris already, and each cause has a clear fix at fitting time rather than later.
Keep the cover clean so the filter keeps working
A guard collects the debris that the intake would have swallowed, and that collection is the point of the guard. Rinse the sponge or sleeve once a week in a bucket of water removed from the tank during the usual water change, squeezing the sponge gently until the water in the bucket runs clearer. Avoid rinsing the cover under a hot tap or replacing the cover at every clean, because filter bacteria live on surfaces throughout the system and rough handling removes more than debris. Check flow after each rinse by watching the return and the surface movement, and note any week where the cover clogged faster than usual, because faster clogging often signals heavier stocking, heavier feeding, or a plant shedding leaves near the intake.
Shape the area around the intake
Plants and decor near the intake change how fish meet the current. Place a broad-leaf plant or a piece of decor where it slows a direct swimming lane toward the intake, without pressing against the cover or blocking the flow into it. Keep the area in front of the cover visible from the front glass, so a pinned fish or a trapped fry can be spotted during a normal look at the tank rather than during a weekly clean. When a guppy goes missing, check inside a hang-on filter body and behind the intake cover before assuming the worst, because small fish that slip past a loose cover often survive in the calmer water inside the filter for a time. Rescue any fish found there gently with a soft net, fix the gap that allowed entry, and record where the gap was so the fitting gets checked at that spot in future weeks.
Fry tanks and longer-term choices
A tank that holds fry regularly deserves a longer look at filtration itself. Gentle sponge filtration driven by air has no narrow intake tube and no strong localised draw, which removes the hazard at source while still cleaning the water in a lightly stocked fry tank. Safety here is a habit rather than a single purchase: fit, flow, rinse, and observe, repeated weekly. KinsLe's Care Teams holds the rinse schedule, the flow check, and the cover replacement note as recurring shared tasks, so the intake guard stays part of the tank routine for every keeper.