Aquarium Water Conditioner Guide: Treat Tap Water for Fish

November 6, 2026

An aquarium water conditioner makes tap water safer for fish before you pour it into the tank. Town water is treated so people can drink it, but the same chlorine and chloramine can harm fish and the helpful bacteria in your filter. This guide explains what a conditioner does, when to use it, and which bottles we stock in Australia.

Key takeaways

Keep these five points in mind every time you fill a bucket from the tap. They cover why the product matters, how to dose it, and how it fits with normal water changes and filter care for home aquariums in Australia.

• Treat every new bucket of tap water before it goes into the tank.
• Dose to the bottle label for the litres you are adding, not a guess.
• Chlorine and chloramine protect people, but they are hard on fish and filter bacteria.
• Standing water for about 24 hours may help with chlorine, but chloramine often needs a liquid dose.
• Rinse filter sponges in old tank water, not fresh untreated tap water.

What does a tap water conditioner do?

An aquarium water conditioner (also called a dechlorinator or tap water treatment) is a liquid you add to new tap water. It is made to reduce chlorine and related disinfectants so the water is gentler for fish. Browse our aquarium and fish products range at Mindiampets for the bottles we keep in stock across Australia.

The RSPCA is clear that chlorine in tap water is a problem for both fish and the bacteria that keep a filter working. That is why a dechlorinating product belongs in every water-change routine, not only on day one of a new tank.

Chlorine present in tap water is dangerous to both fish and bacteria. As such, it’s vital to add a dechlorinating product to the new water or leave it standing for 24 hours for the chlorine to leave the water.

RSPCA, Fish environment

Standing water for about 24 hours can help with plain chlorine. Many suppliers also use chloramine, which lasts longer in the pipes. The US EPA notes that more than 20% of people in the United States use drinking water treated with chloramines (more than 1 in 5). Town supplies across Australia vary by council area, so a measured liquid dose is a more reliable habit than waiting and hoping the gas has gone.

Chloramines (also known as secondary disinfection) are disinfectants used to treat drinking water and they: Are most commonly formed when ammonia is added to water containing free chlorine… Provide longer-lasting disinfection as the water moves through pipes to consumers.

US EPA, Chloramines in drinking water

Why treat tap water before it reaches fish?

Drinking water is treated so it is safe for people. The same treatment can stress fish gills and wipe out useful filter bacteria if you pour it straight in. The RSPCA fish care pages stress that water quality matters as much as food. Pair this with our fish food guide for daily care.

The RSPCA fish health advice reminds keepers that poor water is a common source of stress. Preparing new water is one simple step that lowers that risk before fish feel a sudden change in chlorine level.

How to dose conditioner on a water change

Use an aquarium water conditioner every time you add tap water: new setups, weekly changes, and small top-ups. Measure the litres in your bucket, then add the dose on the bottle. Mix for about 10 to 30 seconds, then pour the water in slowly over 1 to 2 minutes.

The RSPCA also suggests matching temperature so fish are not shocked by a sudden cold or hot fill. A spare heater in the change bucket can help on larger changes of 20 litres or more. For a full first-tank walkthrough, Fishkeeping.co.uk has a clear set-up guide you can follow beside your Tetra AquaSafe, API, Aquasonic or Blue Planet bottle.

Conditioner options we stock

We stock several in-stock aquarium water conditioner bottles and related water-care products from Tetra, API, Aquasonic and Blue Planet. Always read the label for dose and tank type. We do not make medical claims about disease treatment here. These products are for preparing tap water and supporting normal water care.

• Tetra AquaSafe PLUS: a tap water treatment for fresh and marine aquariums. A familiar dechlorinator used on water changes.
• API Tap Water Conditioner 118ml: a compact bottle for treating chlorine and chloramine in tap water.
• Aquasonic Power Water Conditioner: an Australian aquarium tap-water treatment for regular changes.
• Blue Planet Water Conditioner: removes chlorine and chloramine from tap water and adds electrolytes as labelled.
• API Quick Start 118ml: used when you want extra support for a new or restarted filter, as directed on the pack.
• API Freshwater pH Test Kit: helps you check pH after changes so you can see if water stays steady.

All of the products above are in stock at the time of writing. Start with one bottle that matches your tank size, then keep a test kit handy if you want to watch pH after bigger changes. See the full aquarium products category for more water-care options from the same brands.

Water changes and filter care

The RSPCA links water changes to keeping nitrate under control after the biological filter has done its work on ammonia and nitrite. Condition new water every time, and keep the weekly rhythm steady so waste does not spike between cleans.

This is why you need to carry out weekly 30% water changes to dilute the waste products your biological filter cannot break down.

RSPCA, Fish environment

A common pattern is about a 30% change each week, but always match the size of the change to your stock and test results. Treat every litre of new tap water with aquarium water conditioner before you put it back in. On a 100 litre tank, that is about 30 litres of treated water each week. On a 40 litre nano tank, that is about 12 litres. Larger display tanks of 200 litres need about 60 litres for the same 30% change.

When you clean filter sponges or media, rinse them in a bucket of old tank water you just removed. Fresh untreated tap water can kill the bacteria living on that media. The RSPCA warns that rinsing under the tap can wipe out the helpful bacteria your filter needs.

Dechlorinator vs other water products

It helps to keep roles clear so you do not double-dose or skip the step that matters most for chlorine and chloramine. Use one product for tap water, and only add starters or pH tools when the label and your tests say you need them.

Food and water care work together. After you sort aquarium water conditioner and changes, use our fish food guide and fish food range to match flakes or pellets to your fish. Keeping goldfish? See our goldfish food guide.

How much do you need per bucket?

Dose aquarium water conditioner by the litres of new water, not by the full tank size, unless the label says otherwise. A 20 litre change needs the dose for 20 litres. A new empty 60 litre tank needs the dose for all 60 litres.

Many bottles use about 5 ml per 10 to 50 litres depending on brand strength, so always check your own Tetra AquaSafe, API, Aquasonic or Blue Planet label. A 100 ml to 118 ml bottle often covers weeks of small changes on a single home tank at Mindiampets stocking levels.

If you top up 2 to 5 litres every few days, still add a proportional drop. Evaporation leaves minerals behind and you are still adding fresh tap water, so the disinfectant load still matters. A 5 litre top-up is only about 5% of a 100 litre tank, but it still needs a dose.

Common mistakes to avoid

Most water problems after a change come from a few simple skips. Check this list before you tip the next bucket into a stocked tank, and you will avoid the errors we see most often in new setups.

• Pouring untreated tap water straight into a stocked tank.
• Guessing the dose instead of reading the ml-per-litre chart.
• Rinsing filter media under the kitchen tap.
• Changing more than about 50% of the tank in one go without matching temperature.
• Using pond or garden chemicals that are not made for aquariums.

Specific questions about aquarium water conditioner

These short answers cover the questions Australian keepers ask most about dosing, overnight standing water, shrimp tanks, bottle size, and whether conditioner replaces filters or tests.

Do I need it for every water change?

Yes. Every time you add tap water, dose aquarium water conditioner for those litres. It takes under 1 minute and it protects both fish and filter bacteria from chlorine and chloramine.

Can I just leave tap water out overnight?

Standing water for about 24 hours can help with some chlorine, as the RSPCA notes. Chloramine often stays longer in the water supply. That is why a liquid aquarium water conditioner is the safer everyday method in most homes.

Is it safe for shrimp and live plants?

Most community freshwater products from Tetra, API, Aquasonic or Blue Planet are made for mixed tanks. Check the label for any notes about invertebrates or planted tanks, and dose only as directed.

What size bottle should I buy?

Buy for how often you change water and how many litres you move each week. A 118 ml API bottle suits one small tank. A larger Tetra or Blue Planet bottle suits several tanks or big weekly changes of 30 litres or more.

Does it replace a filter or water tests?

No. An aquarium water conditioner prepares new tap water. You still need a working filter, sensible stocking, and tests when you want to check ammonia, nitrite, nitrate or pH with a kit such as the API freshwater pH test.

References

1. RSPCA — Fish environment (chlorine and water changes)
2. RSPCA — Pet fish advice
3. RSPCA — Fish health
4. US EPA — Chloramines in drinking water
5. Fishkeeping.co.uk — How to set up an aquarium

Looking for a monthly treat bundle for the rest of the household pets? See our pet subscription box.

Dr Jay Rollings BSc DVM

Veterinarian – Dr Jay Rollings is a skilled veterinarian with 12 years experience in wildlife research and conservation

During veterinary school, he contributed to projects involving species such as hammerhead sharks, Shark Bay mice, woylies, mulgara, and kangaroos, gaining valuable hands-on experience in wildlife health and preservation.