Step-by-step
Step 1: Turn off equipmentUnplug heater, filter, and powerheads. Heaters can crack if exposed to air while hot. Filters can lose prime.
Step 2: Vacuum substrateInsert the gravel vacuum into the substrate. Pinch and release to siphon water + lift detritus. Move across the substrate, focusing on uneaten food + waste hot spots.
Step 3: Drain to target volumeFor weekly maintenance: 25-30% (10 gallons from a 40g tank). For nitrate spikes: up to 50% maximum. Larger water changes need to be split over multiple days.
Step 4: Prepare replacement waterSaltwater: mix new RODI + salt to match display SG (1.025). Freshwater: dechlorinate tap water with Prime per dose instructions. Match temperature within 2°F using a thermometer.
Step 5: Refill the tankPour slowly to avoid disturbing aquascape. Use a clean pitcher or pump for large tanks. Saltwater systems benefit from filling with a powerhead running.
Step 6: Restart equipmentPlug heater + filter + powerheads back in. Verify filter primes (canister filters may need a manual prime). Watch for 5 minutes before walking away.
Step 7: Test parametersAfter 1 hour of equipment running, test ammonia + nitrite + nitrate. Verify they match expected post-water-change levels (lower nitrate by ~25-30%).
Frequently asked questions
How often should I do a water change?
Weekly 25-30% is standard for most tanks. Reef tanks: 10-15% weekly. Shrimp tanks: 10% weekly with carefully parameter-matched water. Always test rather than relying on a calendar.
Can I do too much of a water change?
Yes - changes >50% can shock livestock from sudden parameter shift. Split larger nitrate corrections over 2-3 changes spaced 2-3 days apart.
Do I need to dechlorinate water?
Yes for tap water (Prime, AmQuel+, or similar). RODI + saltwater mix does not need additional dechlorinator if the source RODI is clean.