How Often Should You Change Aquarium Water? | Beginner Fishkeeping Guide

Keeping an aquarium healthy comes down to one simple habit: regular water changes.

If you’re new to fishkeeping, you might be wondering:

How often should I change my aquarium water?

For most aquariums, the general rule is simple:

Change 20–30% of your aquarium water once per week.

This routine helps remove waste, maintain water quality, and keep fish healthy. But the ideal schedule can vary depending on your tank size, fish species, filtration, and plants.

In this beginner-friendly guide, we’ll explain why water changes matter, how often to do them, and how to perform them properly.

Why Water Changes Are Important in Aquariums

In nature, fish live in huge bodies of water where waste is constantly diluted and filtered naturally.

Your aquarium, however, is a closed environment.

Fish produce waste, uneaten food decomposes, and plant debris breaks down. This releases substances like:

• Ammonia
• Nitrite
• Nitrate

Beneficial bacteria in your filter help convert harmful ammonia into less harmful nitrate. But over time, nitrate builds up in the water, which can stress fish and contribute to algae growth.

Regular aquarium water changes help by:

• Removing excess nitrate and waste
• Replenishing essential minerals
• Improving water clarity
• Supporting healthy fish and plant growth

Think of water changes as refreshing your aquarium’s ecosystem.

How Often Should You Change Aquarium Water?

The frequency of aquarium water changes depends on several factors including tank size, stocking level, and filtration.

Here are some simple guidelines for beginners.

Small or Nano Aquariums (Under 40 Litres)

Smaller aquariums can become unstable quickly because waste builds up faster in a small volume of water.

Recommended schedule:

25–30% water change every 5–7 days

Nano tanks require a little more attention, but with regular maintenance they can thrive.

Medium Community Aquariums (60–150 Litres)

This is the most common aquarium size for beginner fishkeepers and offers a good balance of stability and manageability.

Recommended schedule:

20–30% water change once per week

Weekly changes help maintain consistent water parameters and healthy fish.

Large Aquariums (200 Litres or More)

Larger tanks dilute waste more effectively, meaning water quality changes more slowly.

Recommended schedule:

20–30% water change every 1–2 weeks

However, tanks with a high number of fish may still benefit from weekly changes.

Heavily Stocked Tanks or Messy Fish

Some species produce significantly more waste.

Examples include:

• Goldfish
• Large cichlids
• Certain catfish

These aquariums require more frequent maintenance.

Recommended schedule:

30–40% water change every week

Good filtration and regular water changes are essential for these fish.

Planted Aquariums

Live plants naturally absorb nitrate, which can help maintain water quality.

For most planted tanks:

20–30% weekly water changes work well.

High-tech aquascapes using fertilisers and CO₂ injection may require more frequent changes to maintain nutrient balance.

Signs Your Fish Tank Needs a Water Change

Even with a regular schedule, it’s important to watch for signs that your aquarium may need attention.

Common indicators include:

• Cloudy water
• Rapid algae growth
• Fish spending time near the surface
• Unpleasant odours
• High nitrate readings during water tests

If something looks off, performing a partial water change is often the safest first step.

How to Change Aquarium Water (Step-by-Step)

Once you get used to it, a water change usually takes 10–15 minutes.

Follow these simple steps:

1. Turn Off Aquarium Equipment

Switch off heaters and filters before removing water if necessary to prevent damage.

2. Remove Water with a Siphon

Use a gravel vacuum or siphon to remove around 20–30% of the water while cleaning debris from the substrate.

3. Prepare Fresh Water

Ensure conditions of fresh water are similar to tank water. Always add a water conditioner to remove chlorine and chloramines from tap water.

4. Refill the Aquarium

Slowly add the treated water back into the tank to avoid disturbing fish or substrate.

5. Turn Equipment Back On

Restart your heater and filter (if necessary) once the water level is restored.

Your aquarium now has fresh, clean water for your fish.

Common Water Change Mistakes Beginners Make

Changing Too Much Water at Once

Replacing more than 50% of the water can stress fish and disrupt beneficial bacteria.

Smaller, regular changes are much safer.

Cleaning Everything at the Same Time

Avoid deep cleaning the substrate, filter media, and decorations all in one session.

Too much cleaning can remove beneficial bacteria that keep your aquarium stable.

Forgetting Water Conditioner

Tap water contains chlorine and chloramine, which are toxic to fish and beneficial bacteria.

Always treat new water with a quality dechlorinator.

The Secret to a Healthy Aquarium

• The most successful aquariums aren’t complicated, they’re consistent.

A simple weekly water change routine helps maintain:

• Stable water parameters
• Healthy fish
• Clear water
• Balanced plant growth

Over time, this routine becomes a quick and easy part of fishkeeping.

Need Help Maintaining Your Aquarium?

If you’re unsure about your aquarium’s water quality or maintenance schedule, the team at Newtown Aquarium is always happy to help.

Visit us for:

• Professional aquarium water testing
• Expert advice for beginner fishkeepers
• Aquascaping inspiration
• Quality filtration and maintenance equipment
  

A healthy aquarium starts with the right knowledge and we’re here to help every step of the way.