The Complete Guide to Weekly Water Changes

June 18, 2026

By The Glass and Gill – Aquascape

If there’s one habit that separates average aquariums from truly thriving ones, it’s this: consistent, proper water changes.

No matter how advanced your filtration system is, nothing replaces the power of fresh, clean water. Weekly water changes are essential for maintaining healthy fish, stable water parameters, and crystal-clear aquascapes.

In this guide, we’ll walk you through the correct way to perform water changes, while avoiding the most common mistakes that can harm your tank.

🌊 Why Water Changes Are So Important

In a closed aquarium system, waste constantly builds up:

Fish produce waste
Uneaten food decomposes
Organic matter breaks down

This leads to the buildup of harmful substances:

Ammonia (highly toxic)
Nitrites (toxic)
Nitrates (less toxic, but harmful over time)

While your filter converts ammonia into less harmful compounds, nitrates will continue to rise.

👉 The only reliable way to remove nitrates is through regular water changes

✅ Benefits of Weekly Water Changes

Consistent water changes help:

✔ Remove toxins and waste
✔ Keep fish healthy and stress-free
✔ Improve water clarity
✔ Support plant growth
✔ Stabilise water chemistry
✔ Reduce algae buildup

👉 Clean water is the foundation of every successful aquarium

⏱️ How Much Water Should You Change?

A general guideline:

20–30% water change every week

However, adjust based on your tank:

Lightly stocked tanks: 15–20%
Moderate stocking: 20–30%
Heavy stocking: 30–50%

👉 Consistency is more important than doing large changes occasionally

🧰 What You’ll Need

Gravel vacuum / siphon
Bucket (aquarium-use only)
Dechlorinator
Thermometer

Optional:

Water testing kit
Hose system for larger aquariums

✅ Step-by-Step: How to Perform a Water Change

1. 🛑 Turn Off Equipment

Switch off:

Filter
Heater
Air pumps (if necessary)

👉 Prevents damage and keeps equipment safe during maintenance

2. 🧽 Clean Glass (Optional)

Before removing water:

Wipe algae from glass
Gently clean décor if needed

This allows debris to be removed during siphoning.

3. 💧 Remove Water & Vacuum Substrate

Using a gravel vacuum:

Remove 20–30% of tank water
Clean debris from the substrate
Remove waste and uneaten food

👉 Focus on dirty areas—don’t over-clean everything at once

4. 🌡️ Prepare Replacement Water

Before adding new water:

Match temperature to your tank
Add dechlorinator

🚫 Never add untreated tap water

Tap water contains chlorine and chemicals that can harm fish and beneficial bacteria.

5. 🔁 Slowly Refill the Tank

Add water gently:

Pour slowly
Use a plate or decoration to reduce disturbance
Avoid stirring up substrate

6. ⚙️ Restart Equipment

Turn your system back on:

Filter
Heater
Air systems

Ensure everything is functioning correctly.

⚠️ CRITICAL RULE: Water Change vs Filter Cleaning

This is one of the most important rules in fishkeeping:

👉 Never perform a full filter clean on the same day as a water change

❗ Why This Matters

Your aquarium depends on beneficial bacteria that live in:

Filter media
Substrate
Surfaces in your tank

If you:

Remove water AND
Clean or replace filter media

👉 You risk removing too much beneficial bacteria, which can cause:

Ammonia spikes
Nitrite spikes
Fish stress or death

✅ Best Practice

Follow this simple rule:

Water change day → leave filter alone
Filter cleaning day → no major water change or deep cleaning

👉 Always space these out by a few days

💡 How to Clean Your Filter Safely

Rinse media using tank water (not tap water)
Clean gently—don’t scrub
Never replace all media at once

🔥 Expert Insight

Your filter is the biological engine of your aquarium—protect it, and your system stays stable.

⚠️ Common Mistakes to Avoid

❌ Changing too much water at once
❌ Forgetting dechlorinator
❌ Using incorrect temperature water
❌ Cleaning everything at once
❌ Skipping maintenance
❌ Over-cleaning substrate

👉 These mistakes can destabilise your tank quickly

🧠 Pro Tips from The Glass and Gill

✅ Stick to a weekly schedule
✅ Use a gravel vacuum each time
✅ Test your water regularly
✅ Keep routines consistent
✅ Avoid overfeeding (reduces waste buildup)

🌿 Special Note for Planted Tanks

If you run a planted aquarium:

Plants help absorb nitrates
Avoid excessive substrate cleaning
Maintain balance between plant growth and water changes

👉 Plants support the system—but don’t replace water changes

🐟 Signs Your Tank Needs a Water Change

Watch for warning signs:

Cloudy water
Fish acting stressed
Algae growth increasing
Bad odours
High nitrate readings

👉 Don’t wait for problems—prevent them

💡 Quick Summary

👉 Remove → Replace → Restore

That’s the foundation of every successful water change.

🌱 Final Thoughts

Weekly water changes are simple—but they are one of the most powerful tools in aquarium keeping.

Done correctly, they ensure: ✔ Healthy fish
✔ Stable water
✔ Clear aquascapes
✔ Long-term success

At The Glass and Gill – Aquascape, we believe success comes from mastering the fundamentals. Stay consistent, respect your system, and your aquarium will thrive.