Why water changes matter
Even a perfectly cycled tank steadily accumulates nitrate, the end product of the nitrogen cycle, along with dissolved organics and depleted minerals. No filter removes nitrate on its own. A regular partial water change is the only reliable way to dilute it, replenish minerals and keep your water stable. It does more for fish health than any additive on the shelf.
How much and how often
For most stocked tropical community tanks, a 25–30% change once a week is the reliable baseline. Rather than obey a fixed rule, let your nitrate reading decide: test weekly with a liquid test kit and aim to keep nitrate comfortably below 20–40 ppm. If it creeps up, change more or more often; if it stays low in a lightly stocked planted tank, you may stretch the interval.
What you need
- A gravel vacuum or hose-fed water changer — the best-value tool in the hobby. See our best gravel cleaner pick and the maintenance hub.
- A clean bucket kept only for aquarium use — never one that has held detergent.
- Dechlorinator to neutralise chlorine and chloramine in tap water.
- A thermometer to match the temperature of the refill water.
Step by step
- Unplug the heater and filter if the water level will drop below them, so they never run dry.
- Vacuum the substrate as you drain. Push the gravel vacuum into the top layer to lift out trapped waste and uneaten food while siphoning water into your bucket.
- Stop at 25–30%. Watch the level so you take out the right amount without exposing fish.
- Prepare the new water. Fill a bucket to a temperature close to the tank (a few degrees is fine), add dechlorinator, and stir.
- Refill gently. Pour slowly onto a plate or your hand so you do not disturb the substrate or shock the fish.
- Restart equipment once the water is back above the heater and filter intake.
Making it painless
The easier the job, the more reliably you will do it. A hose-fed water changer that connects to a tap removes the bucket-carrying entirely and is worth every penny on a larger tank. Keep your kit together in one spot so a water change is a ten-minute routine, not an ordeal. Pair it with a quick filter check and a glance at your test results, and you have a complete weekly maintenance session. If nitrate is stubbornly high even with regular changes, our guide on lowering nitrates covers the other levers.