Guide — Water Change Guide
Water Change Guide
Clean, stable water is the foundation of long-term fish health. Water changes remove dissolved waste, reduce nitrate and reset water chemistry before it drifts out of range.
Done correctly, water changes prevent most water-quality problems before they ever show up on a test kit.
TanksConnected · Routine care
What water changes remove
- Rising nitrates
- Dissolved organic waste
- Fish hormones and trace metals
- pH drift and mineral imbalance
Linked guide: Nitrogen Cycle
Water changes remove nitrate — the final stage of the nitrogen cycle. If you’re not sure how the cycle works, start there so this guide makes more sense.
NITROGEN CYCLE · BACKGROUND SCIENCE
Understand why nitrate only leaves by dilution.
Open nitrogen cycle guide
How often should I change water?
General recommendations
- Community tanks: 25–40% weekly
- Messy fish / cichlids: 40–60% weekly
- Planted tanks: 20–30% every 1–2 weeks
- Quarantine tanks: As often as needed to keep ammonia/nitrite at 0
Use nitrate as your guide
- Keep nitrate under 40 ppm (under 20 ppm for sensitive species).
- Fast nitrate rise = bigger or more frequent changes.
- Stable low nitrate = your tank is well-matched to its stocking.
How to do a safe water change
1. Prepare
- Switch off heater and equipment that may run dry.
- Get siphon, bucket or hose ready.
- Measure water conditioner for the volume you’ll replace.
2. Remove water
- Siphon water into a bucket or straight to a drain.
- Vacuum the substrate lightly without digging too deep.
- Avoid stirring huge waste pockets at once in very dirty/overstocked tanks.
3. Treat and match new water
- Add dechlorinator for the full replacement volume.
- Match temperature within about 1–2 °C of the tank.
- pH from tap is usually stable enough — avoid chasing numbers every change.
4. Refill and restart equipment
- Pour new water gently onto a plate/hand/hardscape to avoid blasting the scape.
- Switch filters and heaters back on immediately.
- Make sure the filter is fully primed and flowing properly.
- Check for leaks and wipe up drips around the tank and hoses.
Filter care during water changes
Protect your bacteria
- Rinse filter sponges and media in old tank water, not straight tap.
- Never use hot tap water on media — it can kill the bacteria instantly.
- Clean only part of the filter at a time to avoid “resetting” it.
- Keep media wet at all times; don’t leave it sitting in air.
Common mistakes
- Changing 100% of the water without a true emergency.
- Washing filter media under hot tap water.
- Skipping changes because “the water looks clear”.
- Adding new fish right after a massive water shift.
- Only topping up evaporation instead of doing real water changes.
Summary
- Water changes remove what your filter can’t.
- Most tanks thrive on regular, weekly partial changes.
- Always dechlorinate new water before it reaches the fish.
- Match temperature and avoid big, sudden swings.
- Filter bacteria are your tank’s life support — don’t nuke them during cleaning.