Changing How Often Aquarium Water Should Be: A Beginner’s Complete Guide
It is probably one of the very first questions any beginner to aquariums may ask: “How often should I change the water?” Some say every day, some once a month, while others never. This confusion leads many beginners into overcleaning the tank or completely ignoring water changes.
The truth is straightforward: water changes in aquariums are a must, but timing is everything. In this guide, you learn how often to change water in an aquarium, how much water should be changed, and why water change is crucial for your fish.
Why Aquarium Water Changes Are Important?
Fish are always in the same water. Their own waste, uneaten food, and dying plant material will gradually contaminate the water. Even with a filter, toxic substances such as ammonia and nitrate will accumulate over time.
Regular water changes will help to:
Fish waste removal
Reduce hazardous chemicals
Add fresh oxygen
Keep fish healthy and active
Prevent bad smell and cloudy water
A clean tank doesn’t mean only crystal-clear water, but it also means safe water chemistry.
How often is the changing of water in the aquarium recommended?
There is not one answer for every tank, but to the uninitiated, this rule works best:
General Rule (Most Tanks)
Replace 20–30% of the water every week
This routine will keep the water stable and safe without stressing the fish.
Water Change Schedule Based on Tank Size
Small Aquariums (20–40 liters)
The small ones get dirty much faster.
Change 25–30% water every 5–7 days
Small mistakes show very quickly in small tanks; because of this, regular water changes are extremely important.
The Medium Aquariums: 50–100 liters
Change 20–25% water once a week
These tanks are more stable but still need care on a weekly basis.
Large Aquariums: above 100 liters
Change 15–20% water every 7–10 days
Larger tanks hold more water, therefore the waste spreads out slower.
New Tank vs Old Tank Water Changes
New Aquarium (First Month)
In a new tank, it is still growing beneficial bacteria.
Change 10–15% water once a week
Avoid large water changes
Do not clean filter media completely
Too much cleaning can disrupt the cycling process.
Established Aquarium (After 1–2 Months)
Once your tank is stable:
Follow regular weekly change of 20-30%
Tank will remain clear and well-balanced.
How Much Water Should You Change?
Never drain all of the water out except in absolute emergency situations.
Avoid These Mistakes ❌
Change 100% water
Changing 70–80% water regularly
Cleaning filter and gravel at the same time
Large water changes shock fish and kill the good bacteria.
How to Change Aquarium Water: Step-by-Step Instructions
Step 1: Switch off electrical appliances at the socket.
Switch off filter and heater before start.
Water should be drained off gradually.
Siphon the water off or use a pipe to drain it out of the tub carefully.
Lightly vacuum the gravel.
Remove waste from the bottom of the fishes
Step 3: Refresh with New Water
New water should:
Same temperature as the water in the tank
Be treated with conditioner
Clean and chlorine-free
Never add raw tap water directly into the tank.
Water should be added gradually.
Pour water gently, avoiding shaking the fish and plants.
Turn equipment back on
Step 5: Restart filter/heater after water change.
Signs You Need a Water Change Earlier
Sometimes, water in your tank needs to be changed out of turn.
Watch for these:
Water appears cloudy
Bad smell from the tank
Fish gulping in air at surface
Fish showing stressed behavior or hiding
Excess algae growth
If you notice these signs, change 20–25% of the water immediately.
Do Filters Replace Water Changes?
No. Filters clean the solid waste and help bacteria grow, but they don’t take out all of the nitrate.
The only safe way to remove the built-up chemicals is through water changes.
How Water Changes Help Fish Health
Fish in clean water:
Grow faster
Show brighter colours
Eat healthier
Get sick less often
live longer
Water with filth gradually weakens fish, even though they appear fine from the outside.
Common Beginner Mistakes
Avoid these mistakes:
❌ The complete change of water
❌ Skipping water changes for weeks
❌ With untreated tap water
❌ Overcleaning filter
Final Thoughts
Water changes are the backbone of aquarium care. You don’t need expensive tools or chemicals — just a simple weekly routine. When done correctly, water changes keep your aquarium stable, your fish stress-free, and your tank looking beautiful.
Remember:
👉 Small changes regularly are better than big changes rarely
Once you follow this habit, aquarium maintenance becomes easy and enjoyable.