It is tempting to use tap water for an aquarium or fish tank because of its accessibility and affordability, but how long can fish survive in tap water?

If your tap water is untreated, your fish will only survive a few days, because it contains harmful contaminants that will affect the health of your fish.

However, there is no problem without a solution. Before we delve into that, let’s first understand why ordinary tap water is harmful to your fish.

Why Is Tap Water Harmful to Fish?

Tap water, in most residences, is sourced from the city water facility. The city plant typically uses chemical substances such as chlorine and chloramine to treat your tap water to kill harmful contaminants.

These chemical substances are used to treat drinking water. However, they are also lethal to the beneficial bacteria your fish need to survive.

Chlorinated water is toxic to fish. When your fish is exposed to trace amounts of chloramine and chlorine, they will most likely become ill. Chlorine at high concentrations can even kill your fish.

Factors Affecting Fish Survival in Tap Water

Fish Species, Size, and Metabolism

Certain factors concerning the fish you rear in your fish tank can be a determining factor in their survival. These factors include their species, metabolism, and size.

Studies have observed that larger fish require more oxygen, but they’re more equipped to handle fluctuations in oxygen. This makes them able to survive longer than smaller fish in fish tank water with inadequate oxygen levels.

Also, adult fish can survive longer than young fish in tap water.

In terms of fish species, species such as Cichlids, Archers, Paradise Fish, and Scats can better adapt to water hardness.

Water Stress

Stress levels in water are triggered by bad water conditions can also affect the survival of your fish. Heavy metals, nitrates, and low oxygen are some of the catalysts for stress in water and will eventually prove fatal to your fish.

Also, when your aquarium water has a high ammonia level, it’s caused by the presence of bad bacteria, which eventually results in ammonia poisoning. This usually occurs during the nitrogen cycle.

Water Test

Tap water quality varies depending on your location or region. For survival, your fish require a healthy aquarium. This means your fish tank water should contain balanced levels of minerals, nitrates, and oxygen to ensure your fish live.

When you notice your fish abnormally gasping for air at the surface, it’s a sign that you should test your water to pinpoint the source of the problem. It also means that your fish have depleted the oxygen supply at the lower levels of your aquarium.

There are available fish tank water testing kits for detecting the pH level, the presence of dissolved gas such as ammonia and chlorine as well as other crucial parameters.

Through a water test, you can monitor the parameters of your fish tank water.

How to Treat Tap Water for Fish

Allow the Water to Sit

You can let your tap water settle for at least 1 day to dechlorinate because chlorine gradually evaporates at room temperature. There are instances where it will take a few days before your tap water will completely remove chlorine.

When you let your tap water sit in the tank, it will attain room temperature. The change in surroundings will reduce the stress your aquarium fish is exposed to.

Using a Water Conditioner

Water conditioners are chemical compounds that can neutralize chloramine and remove chlorine from tap water. Some water conditioners can also be used to treat water hardness.

To use it, we recommend applying it to your fish tank before filling it with water and adding fish. There are a lot of reliable water conditioners ranging in different sizes. They are affordable and they make your pet fish safe in tap water.

Heat the Water Before You Fill your Fish Tank

If you’re not patient enough to let the water sit for at least a day to dechlorinate, then this solution is the better option for you. Within 15 minutes, this method won’t just remove chlorine, it will also get rid of the bad bacteria which trigger fish skin ailments.

However, the speed or duration of this process relies on the quantity of water and surface size. So we recommend using wider containers if you want to boil sufficient tap water for a large fish tank. This is one of the effective ways to make your tap water safe for your fish.

Using an Ultraviolet System

A UV unit emits ultraviolet light on your water which neutralizes chlorine, helps you eliminate organic matter such as algae, and breaks down toxic substances such as nitrates and ammonia.

However, this solution has its limitations as well. It may not change the state of your hard water and it’s also not effective in eliminating dissolved solids from your tap water. Despite its limitations, the UV system is effective enough to help your fish survive in tap water.

We recommend getting a good system that can serve you for large tanks and is quick in clearing green or cloudy water.

Reverse Osmosis Filtration

The RO filter connects to your faucets and gets rid of harmful impurities in your water. It has a very wide range of filtration because it can remove almost all kinds of contaminants, making your tap water safe for most fish. The only limitation is microbial filtration, which is a forte of ultraviolet filtration.

It helps your water attain optimal pH levels and treats water hardness since it can also filter out dissolved minerals. We recommend this solution for tropical fish breeders residing in areas known for hard water.

To get the best out of this filter, let the filter run for a few hours before you refill your tank. The reverse osmosis system is very effective in maintaining good water quality for your fish.

Can Fish Remain Alive Without Oxygen Pump?

If your aquarium filter doesn’t agitate the water surface, you may need to install a filter that provides surface agitation. Alternatively, you can combine your filter with an air pump or air stone. These power filters inject oxygen into your water through surface agitation.

Final Thoughts

Tap water is perceived as “clean water” and because it’s okay for human consumption, it’s easy to naturally assume it will be great for your fish. However, tap water contains elements that are considered toxic to your fish. The minerals, ammonia, nitrate, chlorine, and chloramine in your tap water are capable of making your fish sick and killing them.

That’s why we recommend solutions such as letting the water gradually dechlorinate for at least 24 hours, boiling it, or using a filter to make your water ideal for your fish.

About the Author

Lucas Greer

Lucas vs. Wild - Lucas is a true nature lover and survivalist. When he's not teaching science at school, he can be found in nature, hiking, climbing, camping, and rafting. He knows all the tricks and DIYs for making unclean water drinkable with simple means in an emergency. At school, his students love him for his exciting water filtration projects.

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