Can You Use Tap Water to Fill an Aquarium?

Tap water is essential for setting up a new tank but must be treated to protect all freshwater fish from chemicals such as chloramine and metals.

May 22, 2025byLisa Szymanski

can you use tap water to fill aquarium

 

Starting an aquarium hobby is interesting and exciting, but the survival of your fish depends on getting the basics right. All freshwater aquariums are filled with tap water, but a product called dechlorinator is used to treat the water and remove harmful chemicals. While it’s convenient to use tap water, chemicals such as chloramine and metals can make fish extremely ill, often leading to death.

 

This guide looks at the do’s and don’ts of setting up an aquarium, from using tap water to picking the right substrate and filtration systems.

 

Why Treat Tap Water Before Filling an Aquarium?

bubble eye goldfish
A black bubble-eye goldfish. – Credit: Pixabay

 

To make tap water safe for humans, it’s treated with chemicals such as chlorine and chloramine that fish cannot tolerate. Chlorine is dangerous to our finned companions because it harms their gills and increases stress. Exposure to the smallest amounts of chlorine can burn their gills and affect their immunity. Chloramine is a mixture of ammonia and chlorine and is just as harmful as chlorine. In addition to these chemicals, tap water contains small amounts of metals, and while it’s considered safe for human consumption, it’s toxic to fish.

 

Treating tap water is a simple and effective way of removing harmful substances while guaranteeing water quality. To treat and prepare water for a freshwater aquarium, you need a dechlorinator. The dechlorinator works by removing the chemicals and making the tap water safe for your fish. You would use the dechlorinator, otherwise called anti-chlorine, when setting up a new tank and when cleaning the aquarium and adding new water.

 

Invest in a Good Aquarium Filter

community tank with filter
A community tank with a filter. – Credit: Perfect Aquatics

 

Once you’ve purchased a dechlorinator, ensure that your filtration is adequate for the tank size and the type of fish you’ll be housing. The purpose of good filtration is to keep the water moving, remove toxins, and aerate the water. One of the most toxic parameters in a fish tank is ammonia. Ammonia results from decayed food and organic matter that aren’t removed from the tank. A filter plays a vital part in removing the debris to keep the water as clean as possible. Of course, this doesn’t mean that you can skip water changes. It simply means that less frequent water changes need to be performed to prevent ammonia, nitrates, and nitrites from hurting your fish.

 

Choosing the Right Substrate

pleco on gravel
A pleco atop gravel. – Credit: Pixabay

 

You may not give much thought to the substrate of your new tank, but some types can cause serious damage to fish. If you are thinking of adding live plants, aquarium sand is recommended. Without live plants, this type of sand is not the best idea as it may create anaerobic compartments that produce hydrogen sulfide. The foul-smelling hydrogen sulfide is toxic to fish.

 

The best type of gravel is small, dark, and free of artificial colors that would irritate fish. I prefer sand for bottom dwellers with delicate barbels and mouths, such as zebra loaches and clown loaches. In terms of decor, freshwater fish enjoy real plants, while loaches do well with caves, driftwood, and rocks they can hide in.

 

Always clean your aquarium decor with regular water. If you are using driftwood and rocks, place them in boiling water for at least 10 minutes to remove pathogens. Once cool, scrub the remaining debris off the surface and incorporate these natural pieces into your tank.

 

Aquarium Maintenance Promotes Your Fishes’ Well-being

small fish tank
A small freshwater aquarium. – Credit: Unsplash

 

A common question in the aquarium world is just how often you should be changing the water in the tank. I usually perform a partial water change every second week because I have a fairly strong filtration system. If I notice algae growth or I’m managing a condition such as fin rot in the tank, water changes are increased to once a week.

 

To start with, you can change 25% to 50% of the water every two weeks. Never remove all the water from the tank, or you could cause it to crash, which is detrimental to new fish. Cycling allows good bacteria to establish themselves in the aquarium, which combats high levels of ammonia. When you add clean tap water, whether 25% or 50% water changes, always add your chlorine removal product to make the water safe for your fish.

 

Do’s and Don’ts of Setting Up an Aquarium

school of danio
A school of danio. – Credit: Unsplash

 

The most exciting part of setting up a new fish tank is adding your fish. But before you rush out to get your freshwater companions, allow the tank to run for at least three days beforehand. The next step is to test the water for ammonia, nitrates, and nitrites that threaten fish. You can purchase a test kit from your local fish store.

 

Many beginner fishkeepers make the mistake of tossing new fish into the tank, but this can cause shock. Place the bag of fish into the tank and leave them to adjust to the temperature for 20 to 30 minutes. Add a small amount of the tank water to the bag and slowly release them into the water.

 

Rinse the filter sponges or cartridges when you clean the tank. Some believe in rinsing the filter media in dechlorinated water to prevent destroying good bacteria. Lastly, when evening approaches, turn the aquarium light off to mimic the normal day and night cycles that freshwater fish experience in the wild. Following these steps provides simple ways to create an ideal habitat for your aquatic pets.

 

 

 

Lisa Szymanski
byLisa Szymanski

Lisa is a wildlife enthusiast who enjoys hiking and gardening and has four years of experience volunteering at pet shelters. She is the proud mom of two dogs, a Pitbull named Ragnar, a Boerboel named Blueberry, and four feisty chickens, or as she calls them, the \"queens of the yard,\" Goldie, Gray, Peaches, and Brownie.