How to do an aquarium water change
A regular partial water change is the backbone of aquarium maintenance. It dilutes nitrate and dissolved organics, replenishes minerals, and resets the water your fish live in — no filter or additive replaces it.
For most stocked tanks, changing 20–30% of the water once a week keeps parameters stable. Heavily stocked or planted tanks may need more; lightly stocked tanks, a little less.
Steps
Prepare replacement water
Mix fresh water to the same temperature as the tank. For freshwater, dechlorinate tap water; for saltwater, mix to the tank’s salinity and let it stabilise.
Match temperature within ~1°C — a sudden swing stresses fish far more than the water change itself.
Turn off heaters and pumps
Switch off the heater and any pumps that could run dry as the level drops. This protects equipment while the water is low.
Siphon out 20–30% of the water
Use a gravel vacuum to remove water while pulling detritus out of the substrate. Aim for one quarter of the tank volume for a weekly change.
Refill slowly
Add the prepared water gently so you don’t uproot plants or stress fish. Pour onto a plate or your hand to break the flow.
Restart equipment and log it
Turn the heater and pumps back on once the water covers them. Record the change in Aquairi so your schedule and Health Score stay accurate.
Log water testpH8.1Ammonia0.0Nitrite0.0Save reading
Frequently asked questions
A weekly 20–30% change suits most community tanks. Test your nitrate between changes — if it climbs above ~40 ppm, change more often or a larger volume.
Avoid it. Rinsing the filter and changing water together can disturb too much beneficial bacteria at once. Clean the filter on a separate day, in old tank water.
No. For a partial change the fish stay in the tank. Removing them adds stress and is only needed for a full teardown.
Related guides
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