Aquarium Water Changes: How Often and How Much
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Your filter doesn't remove everything. Nitrate builds up, and the University of Florida says "water changes ... are needed to remove nitrate." Here's how different sources size the job.
What sources recommend
| Source | Recommendation |
|---|---|
| Aqueon (goldfish and filtered betta tanks) | 10% weekly or 25% every 2 weeks |
| Habitattitude (USFWS/NOAA-backed) | Up to 20% weekly for tanks with many fish |
| Penn State classroom guide | About one-fourth weekly |
| Python (maker) | 5 to 10% every other week |
| UF, when ammonia is present | 25% to 50% to remove some ammonia |
Aqueon's betta guide adds: in small unfiltered containers, change a third every 3 to 4 days, and "Never change all of your betta's water at one time!"
How to tell if it's enough
Test. Aqueon says nitrate above 50 ppm is "undesirable" and that some tap water is high in nitrate, so test your tap too. If nitrate keeps climbing, change more or more often. See test kits.
Step by step
- Unplug the heater and filter if the water level will drop below them (follow their manuals).
- Siphon water out while vacuuming the gravel.
- Prepare new water at about the same temperature; Aqueon warns against sudden temperature changes.
- Treat it with conditioner. The EPA says chlorine and chloramine must be neutralized.
- Refill slowly, then plug equipment back in.
Hygiene
The CDC suggests wearing gloves when cleaning the tank, especially if you have cuts on your hands, dumping water in a bathtub, laundry sink or outside rather than a kitchen sink, and not letting children under 5 clean the tank. Wash your hands afterward.
Tools
Aqueon Siphon Gravel Cleaner, Medium 9 in.
- For aquariums 15 to 35 gallons, per the listing
- Self-priming: up-and-down motion starts flow
- 6 ft hose with bucket clip
Python No Spill Clean and Fill (50 ft)
- Drains and refills from a faucet, per the listing
- Adapts to most faucets
- Complete ready-to-use system
Seachem Prime (250 mL)
- Removes chlorine and chloramine, per the listing
- Detoxifies ammonia and nitrite at typical tap-water levels
- 5 mL treats 50 US gallons of new water
More in gravel vacuums and water changers.
Filter maintenance
Don't swap all your filter media at once. Fluval's BioMax listing says to replace only half at a time "to allow proper seeding." The University of Florida also warns that some medications, especially antibiotics, can harm the biofilter.
FAQ
How often?
Roughly 10-25% every week or two; test to fine-tune.
Why, with a filter?
To remove nitrate.
All at once?
No.