How to Do a Water Change: The Most Important Aquarium Skill

How to Do a Water Change: The Most Important Aquarium Skill

If you could only do one thing to keep your fish healthy, it would be regular water changes. No filter, no additive, no piece of equipment replaces the simple act of removing old water and replacing it with clean, treated water.

Water changes dilute accumulated waste products — nitrate, dissolved organics, hormones and trace toxins — that your filter cannot remove. They replenish essential minerals and maintain stable water chemistry. Skipping water changes is the slow road to sick fish and algae problems.

This aquarium water change guide walks you through the process step by step, with specific advice for Singapore’s tap water.

Why Water Changes Matter

Your aquarium is a closed system. Fish eat, produce waste, and that waste is processed by bacteria into nitrate. But nitrate does not disappear — it accumulates. Dissolved organic compounds, fish hormones, tannins and other substances also build up over time.

The only way to remove these is to physically take old water out and replace it with clean water. Think of it like opening the windows in a stuffy room — the room does not clean itself, but fresh air makes everything better.

Regular water changes:

• Keep nitrate levels manageable (ideally below 20-40 ppm)
• Remove dissolved organic compounds that discolour water and fuel algae
• Replenish trace minerals that plants and fish need
• Stabilise pH, which can drift over time in a closed system
• Reduce the concentration of fish hormones that can inhibit growth

How Much and How Often

The standard recommendation for most community and planted aquariums is:

• Amount: 20-30% of the tank volume
• Frequency: Once per week

This strikes a balance between effective waste removal and minimal stress to your fish. Changing too much water at once (more than 50%) can cause pH and temperature swings that stress sensitive species. Changing too little does not remove enough waste to make a difference.

Some situations call for different schedules:

• Heavily planted high-tech tanks: 30-50% weekly — more nutrients are dosed, more waste is produced
• Lightly stocked low-tech tanks: 20% weekly or 15-20% fortnightly may suffice
• New tanks (first 4-6 weeks): 20-30% every 2-3 days during cycling to manage ammonia and nitrite spikes
• Breeding tanks: Daily small changes (10-15%) for optimal fry health

Equipment You Need

• Siphon / gravel vacuum: A tube with a wide nozzle that drains water while vacuuming debris from the substrate. Available at any fish shop for $8-$20 SGD
• Bucket: A dedicated aquarium-only bucket (never use one that has held soap or chemicals). 10-15 litre buckets work well for most tanks
• Water conditioner: Essential for treating tap water. Seachem Prime is the gold standard in Singapore
• Thermometer: To match the temperature of new water to your tank
• Towels: Spills happen. Be prepared

For larger tanks (200 litres and above), consider investing in a Python water changer or similar system that connects directly to your tap. This eliminates the need to carry heavy buckets back and forth.

Step-by-Step Guide

1. Turn off equipment: Switch off heaters (if applicable) and any equipment that could be exposed when the water level drops. Filters can usually stay running
2. Prepare your siphon: Start the siphon by either using a squeeze bulb, submerging the entire tube and then lifting one end, or using the quick-start method (a few sharp pumps of the large end)
3. Drain water into a bucket: Direct the narrow end of the siphon into your bucket. Save some of this old water if you plan to clean your filter today
4. Vacuum the substrate: While draining, use the wide end of the siphon to gently push into the gravel or hover above the substrate (see gravel vacuuming section below)
5. Stop at 20-30%: Mark your tank with a small piece of tape to show the target water level, or simply eyeball it with experience
6. Prepare new water: Fill your bucket with tap water and add water conditioner (Seachem Prime: 1 ml per 200 litres, or roughly 2 drops per 10 litres)
7. Match temperature: Adjust the tap water temperature to within 1-2 degrees of your tank. In Singapore, room-temperature tap water (around 28-30 degrees Celsius) is usually close enough for tropical tanks
8. Add new water slowly: Pour the treated water gently into the tank. Pouring onto a flat surface (a plate or your hand) prevents disturbing the substrate
9. Restart equipment: Turn heaters and any other equipment back on
10. Clean up: Wipe any splashes and dispose of the old water (it is excellent for watering plants)

Treating Singapore Tap Water

This is critically important. Singapore’s tap water is treated with chloramine, not chlorine. This matters because:

• Chlorine dissipates naturally if you let water sit for 24 hours or agitate it
• Chloramine does not dissipate on its own. It is a stable compound (chlorine bonded to ammonia) specifically designed to persist in the water supply

You cannot make Singapore tap water safe by simply letting it sit overnight. You must use a water conditioner that specifically neutralises chloramine.

Seachem Prime is the most popular choice among Singapore aquarists for good reason:

• Neutralises both chlorine and chloramine
• Detoxifies the ammonia released when chloramine is broken apart
• Also detoxifies nitrite and nitrate temporarily
• Highly concentrated — a 500 ml bottle treats 5,000 litres of water
• Widely available at local fish shops for $15-$25 SGD

Other effective water conditioners include Seachem Safe (powdered version of Prime) and API Tap Water Conditioner. Whatever you use, make sure the label specifically mentions chloramine.

Singapore tap water typically has a pH of 7.0-8.0, which is suitable for most tropical fish without adjustment. The water is soft to moderately soft (GH 1-4 dGH), which is ideal for many Southeast Asian species but may need supplementation for livebearers and African cichlids.

Gravel Vacuuming Technique

Gravel vacuuming serves two purposes: it removes water for the change, and it extracts debris trapped between substrate particles.

For Gravel Substrates

Push the wide end of the siphon about 2-3 cm into the gravel. The water flow will lift lighter debris (fish waste, uneaten food) while the heavier gravel falls back down. Move the siphon across the substrate in a grid pattern, covering about one-third of the bottom per water change. Over three weeks, you will have vacuumed the entire bottom.

For Planted Tank Substrates (Aqua Soil, Sand)

Do not push the siphon into planted substrates. Hold the nozzle 1-2 cm above the surface and let it hover, picking up debris from the top layer. Disturbing aqua soil can release ammonia and cloud the water. Sand substrates can be gently stirred in unplanted areas, but avoid digging near plant roots.

For Bare Bottom Tanks

Simply hover the siphon along the bottom, picking up all visible debris. Bare bottom tanks are the easiest to clean.

Frequency by Tank Type

Signs You Need More Frequent Changes

• Nitrate above 40 ppm: Your current schedule is not removing enough waste
• Yellow or brown tinted water: Dissolved organics are accumulating
• Persistent algae: Excess nutrients in the water column are fuelling growth
• Fish gasping at the surface: Could indicate poor water quality (test immediately)
• Foul smell: Healthy aquariums have a mild, earthy smell. Anything unpleasant indicates a problem
• pH dropping steadily: Accumulated acids from biological processes are overwhelming the water’s buffering capacity

If you are seeing these signs despite regular changes, increase either the volume or the frequency. Moving from 20% weekly to 30% weekly, or from weekly to twice weekly, can make a significant difference.

Frequently Asked Questions

Can I do too many water changes?

In theory, no — many breeders and competition aquascapers do daily 50% changes with excellent results. In practice, each water change is a minor disruption, so for most hobbyists, once weekly is the right balance between water quality and effort. The exception is new tanks during cycling, where more frequent changes are needed.

Do I need to remove fish during a water change?

No. Removing fish causes far more stress than a gentle water change. Just work slowly and avoid chasing fish with the siphon. They will move out of the way on their own.

Can I use rainwater instead of tap water?

Rainwater in Singapore is very soft and acidic, with little mineral content or buffering capacity. It can be used, but it needs to be collected cleanly (not from roof runoff) and may need mineral supplementation. For most hobbyists, treated tap water is simpler and more consistent.

Is it okay to change more than 50% at once?

Large water changes are fine if the new water is temperature-matched and properly treated. The risk is not the volume itself but the potential for a sudden shift in pH, temperature or mineral content. If your tap water parameters are similar to your tank water, large changes are safe. If they differ significantly, stick to smaller changes.

Water changes are the cornerstone of aquarium maintenance. If you would rather have a professional handle your tank care, Gensou offers regular aquarium maintenance services across Singapore. Contact us to learn more.

Related Reading

• The Complete Water Change Guide: How Much, How Often and Why
• How to Plan an Aquarium Water Change Schedule That Fits Your Life
• How to Set Up an Automatic Water Change System for Aquariums
• How to Set Up a Drip Water Change System
• Top Up vs Water Change: What’s the Difference and Why It Matters