There is no universal water-change percentage. A useful schedule is based on what accumulates in this aquarium and how stable replacement water can be.
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Filtration processes waste but does not make every dissolved compound disappear. Fish waste, leftover food, and biological activity continue to add material until plants use it or maintenance removes it. Water changes dilute that accumulation and replenish some minerals.
Twenty to thirty percent weekly is a reasonable starting point for many community tanks, not a rule. Test nitrate at a consistent point in the schedule and watch the trend. A rapid rise can point to heavy stocking, excess feeding, decaying material, or insufficient plant uptake.
Bigger changes are not automatically better. Shrimp and other sensitive animals can react poorly to abrupt differences in temperature, GH, KH, or pH. Smaller, more frequent changes may be easier on them, and replacement water should be matched as closely as practical.
Substrate cleaning depends on the layout. A bare-bottom or lightly planted tank makes debris easy to remove, while a densely planted aquarium should not have every rooted area disturbed on a schedule. Siphon visible waste and leave healthy root zones intact.
Water changes do not remove the aquarium cycle. Most beneficial bacteria live on filter media, substrate, plants, and hardscape rather than floating in the water. The greater risk is replacing or sterilizing all mature filter media at once.
Keep a simple log of volume, test results, and anything unusual. Test before the change and again at the same point in the next cycle so the comparison is meaningful. Note the replacement-water temperature and volume too, because repeatable inputs make changing trends easier to interpret. Adjust gradually when the trend calls for it. Consistency is more useful than waiting for a visible problem and then making a dramatic correction.
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