Water Changes

Aquarium Water Change Guide

Regular partial water changes remove accumulated waste and replace water with clean, properly prepared water. The process is slightly different for freshwater and saltwater aquariums.

Keep it simple:

Remove part of the old water, clean accumulated debris while the water is draining, prepare the replacement water correctly, and refill the aquarium without causing a major temperature or chemistry swing.

Freshwater Dechlorinate replacement tap water
About 20–30%
A good routine starting point for many aquariums.
Saltwater Match salinity and temperature
About 10–25%
A common routine range depending on the aquarium.

Freshwater Water Changes

For many freshwater aquariums, a partial water change every 1–2 weeks is a good starting routine. Heavily stocked tanks or aquariums with high nitrate may need more frequent water changes.

1
Remove Water About 20–30%
2
Vacuum Gravel Remove trapped debris
3
Condition Water Neutralize chlorine/chloramine
4
Refill Slowly Match temperature

Make Water Changes Easier: Hygger Auto Aquarium Gravel Cleaner

For freshwater aquariums, the Hygger water changer can help eliminate most bucket carrying. It connects to a sink faucet and uses water flow through the faucet attachment to help pull aquarium water through the hose. The same system can then be switched to refill the aquarium.

1. Drain Use the faucet connection to help pull aquarium water through the hose.
2. Gravel Clean Vacuum debris from the substrate while removing the old water.
3. Refill Switch the system and refill the aquarium through the same hose.
Hygger Auto Aquarium Gravel Cleaner
When refilling directly from the faucet: Add enough dechlorinator to treat the replacement water according to the conditioner manufacturer's directions. Make sure the new water temperature is reasonably close to the aquarium temperature.
Useful Freshwater Products: Hygger Auto Aquarium Gravel Cleaner  ·  Seachem Prime  ·  Fresh RODI Water

Should I Vacuum the Gravel?

Gravel can collect fish waste, leftover food and other debris. A water change is an ideal time to remove some of that material before it continues breaking down in the aquarium.

Standard Gravel Aquarium Push the gravel tube gently into one section of the substrate. Allow debris to rise into the tube while the heavier gravel falls back down.
Planted Aquarium Clean more gently around plant roots. Vacuum open areas and remove visible debris without aggressively disturbing the entire planted substrate.
You don't have to deep-clean every inch every time. Cleaning sections of the substrate during routine water changes is often easier and less disruptive than aggressively stirring the entire bottom at once.
Easy Gravel Cleaning: Hygger Auto Aquarium Gravel Cleaner

What Water Should I Use for Freshwater?

Conditioned Tap Water Appropriate for many freshwater aquariums. Use a good water conditioner to neutralize chlorine and chloramine before those disinfectants can harm fish or beneficial bacteria.
RODI Water Useful when keeping species that require low-mineral water or when greater control over water chemistry is needed. Pure RODI may require remineralization depending on the aquarium.
Wet Pets Options: Seachem Prime  ·  Fresh RODI Water

Saltwater & Reef Water Changes

Saltwater changes require one extra step: the replacement water needs to have the correct salinity before it enters the aquarium.

1
Prepare Saltwater RODI + salt mix
2
Match Salinity Especially for reef tanks
3
Match Temperature Avoid sudden swings
4
Remove & Refill About 10–25%

For a mixed reef, replacement saltwater should generally be close to the aquarium's existing salinity. A common reef target is approximately 1.025–1.026 SG.

Wet Pets Water Options: Fresh RODI Water  ·  Pre-Mixed Saltwater  ·  Saltwater Mixing Calculator

Match the Temperature

Replacement water does not need to be mathematically identical to the aquarium, but it should be reasonably close — especially when doing a larger water change.

The larger the percentage of water being changed, the more important temperature matching becomes.

Avoid large temperature swings. Adding a large volume of very cold or very warm replacement water can rapidly change the aquarium temperature and stress livestock.

How Much Water Should I Change?

There is no single percentage that is correct for every aquarium. Stocking level, nitrate accumulation, feeding and maintenance all affect how much water needs to be changed.

Routine Freshwater About 20–30% every 1–2 weeks is a practical starting point for many normally stocked freshwater aquariums.
Routine Saltwater / Reef About 10–25% every 1–2 weeks is a common starting range. Testing and aquarium conditions should guide the final schedule.

If nitrate continues increasing between water changes, consider changing more water, changing it more frequently, reducing excess feeding or addressing the underlying waste load.

Water-change day is a good time to clean mechanical filter media.

Filter floss and dirty mechanical pads can be changed as needed. Established sponges and biological media should generally be preserved rather than replacing everything at once.

View Filter Media Guide

Common Water Change Mistakes

Forgetting Dechlorinator Chlorinated or chloraminated tap water should be properly conditioned before it can harm fish and beneficial bacteria.
Changing Everything at Once Don't combine a large water change with replacing all filter media and completely cleaning every surface.
Large Temperature Swing Replacement water should be reasonably close to the aquarium temperature.
Saltwater Salinity Doesn't Match Check newly mixed saltwater before adding it to the aquarium.
Using Saltwater for Evaporation Evaporation should normally be replaced with freshwater because the salt itself does not evaporate.
Ignoring the Gravel Water changes are more useful when accumulated waste is removed rather than simply taking clear water from the top of the aquarium.
Don't avoid a needed water change just because it is “large.” Routine changes are usually smaller, but an aquarium with a serious water-quality problem may require a larger change. When ammonia, contamination or another emergency is present, improving the water quality is the priority. Make sure the replacement water is properly prepared.
The Simple Wet Pets Water Change:

Remove Water → Vacuum Debris → Prepare Replacement Water → Match Temperature → Match Salinity if Saltwater → Refill

Water-change frequency should be adjusted to the aquarium rather than followed as an absolute schedule. Test the water, watch nitrate accumulation and keep maintenance consistent. Regular partial water changes are one of the simplest ways to maintain stable water quality and a healthy aquarium.