# Aquarium water change schedule

> Pick your tank’s load level and size to get the cadence, percentage, and volume to swap per change. Lightly stocked planted tanks, standard community tanks, and overstocked or messy tanks each follow their own schedule — the comparison table below spells out all three.

Use the interactive scheduler on the page: https://petguidecalc.com/aquarium/water-change-scheduler/. Pick a load level and tank size to get cadence, percent, and volume to swap.

## How often should you change aquarium water?

A standard community tank needs 20% of its water swapped every two weeks. Lightly stocked planted tanks can sit at 10% every two weeks, while heavily stocked or messy tanks need 30% weekly. Enter your load level and tank size below for the exact volume to change.

## Schedules at a glance

| Load level | Cadence | Percent | Swap for 20 US gal | Notes |
|---|---|---|---|---|
| Light | Every 2 weeks | 10% | 2.00 US gal · 7.6 L | Lightly stocked or heavily planted tanks; small bioload produces less nitrate. |
| Standard | Every 2 weeks | 20% | 4.00 US gal · 15.1 L | Default cadence for a typical community tank; matches Instant Ocean’s 20% every 2 weeks example. |
| Heavy | Weekly | 30% | 6.00 US gal · 22.7 L | Overstocked or messy fish (large cichlids, goldfish); weekly changes keep nitrate below 40 ppm. |

Aquarium Co-Op flow drives cadence and percent; Instant Ocean’s 20%/2 weeks is the standard baseline.

## How the schedule is set

Light load — a 10 US gal (≈ 38 L) planted tank swaps 1.00 US gal (3.8 L) per change, matching the light tier row in the table above.

Standard load — a 20 US gal (≈ 76 L) community tank swaps 4.00 US gal (15.1 L) per change.

Heavy load — a 55 US gal (≈ 208 L) overstocked tank swaps 16.50 US gal (62.5 L) per change to keep nitrate below 40 ppm.

## Water change questions, answered

**Q: How often should I change water in a freshwater aquarium?**

Match the tier to your bioload: lightly stocked planted tanks sit at the light tier, typical community tanks at the standard tier, and overstocked or messy tanks at the heavy tier. The schedule table above lists the percent and cadence for each, and the worked examples show the swap volumes for common tank sizes.

**Q: How much water should I change in a planted tank?**

Planted, lightly stocked tanks belong on the light tier. Plants take up nitrate directly, so a smaller, less frequent change still keeps the water chemistry stable — you refresh minerals without stripping nutrients the plants use.

**Q: How often do you change water in an overstocked tank?**

Large cichlids, goldfish, and other heavy-waste setups produce waste faster than twice-monthly changes can handle, so they belong on the heavy tier — the most frequent schedule in the table.

**Q: Should I match the new water temperature to the tank?**

Yes — match the replacement water's temperature to within 2–4 °F (≈ 1–2 °C) of the tank and dechlorinate it before pouring in. A sudden cold or hot change stresses fish; condition only the volume you are changing, which reaches tank temperature quickly in small batches.

**Q: Do I need to gravel-vacuum during a water change?**

Yes for unplanted tanks — gravel vacuuming removes detritus that fuels nitrate. For planted tanks, leave the substrate alone so you don’t disturb root systems; the change alone handles dissolved waste.

## Tools that pair well

- [Aquarium fish compatibility checker](/aquarium/mix-calculator/)
- [Reptile care tools](/reptile/)
- [Hamster cage size calculator](/hamster/cage-size-calculator/)

## Sources

The cadence-per-load flow comes from the Aquarium Co-Op water-change guide and the Instant Ocean example.

- [A nitrogen removal system to limit water exchange for recirculating freshwater aquarium using DHS-USB reactor](https://doi.org/10.1080/09593330.2017.1333530) — Adlin N, Matsuura N, Ohta Y, Hirakata Y, Maki S, Hatamoto M, et al., Environ Technol, 2018.
- [How Often Do You Have to Change the Water in a Fish Tank?](https://www.aquariumcoop.com/blogs/aquarium/water-changes) — Aquarium Co-Op, aquariumcoop.com. Source for the load-level → cadence/percent table (light/standard/heavy).
- [How to Do a Water Change](https://www.aquariumcoop.com/blogs/aquarium/how-to-do-a-water-change) — Aquarium Co-Op, aquariumcoop.com. Practical guide: drain volume, refill temperature match, dechlorinate.
- [Instant Ocean — Salt mix instructions](https://www.instantocean.com/) — Instant Ocean, instantocean.com. 20% every 2 weeks example used as the standard community-tank baseline.

_Educational resource, not veterinary advice. PetGuideCalc — https://petguidecalc.com_