Using tap water in your aquarium & topping up

Why would you need to top up your aquarium water?

Evaporation can lower oxygen levels in an aquarium. Fish swimming closer to the water’s edge than usual or gasping at the surface are sure signs that oxygen levels are too low. Adding new water is a simple way to help bring more oxygen into the tank.

If low oxygen levels are frequent (often in summer months), think about adding some extra aeration, such as an airstone and air pump, to increase oxygen levels.

If you have an open aquarium without a lid you could start using an evaporation tray to decrease the loss of water during the warmer months. 

Is tap water safe for a fish tank?

We use tap water in our homes either to drink or for cleaning. Fish, on the other hand, have different requirements when it comes to water quality.

Tap water can contain chemicals and minerals that may be harmful to fish, such as chlorine, and heavy metals like copper, lead and zinc. Fish need tiny amounts of metal as part of their diet, but too much can be toxic.

They can also have high levels of water hardness or pH which can create an unsuitable environment for certain fish species. Sudden changes in water chemistry can cause stress and may lead to health issues for your fish.

Tap water is safe for your tank so long as you treat it with a water conditioner to remove harmful toxins and chlorine. This could be added for certain situations, such as starting a new aquarium, doing a water change, topping up your aquarium or when adding new fish.

Can I fill my fish tank with tap water?

Tap water is fine for filling up your fish tank so long as you use a tap water conditioner to treat it first. You should also leave the tank for several days before adding fish to allow the water to stabilise.

Before you add any fish it may be worth testing the water to make sure that the parameters (such as pH, ammonia, nitrite, and nitrate levels) are within acceptable ranges for the specific species you plan to keep.

How to make tap water safe for your aquarium

Remember these three important rules when refreshing the water in your freshwater aquarium:

1. Make the water safe for your fish. Treat tap water with Bioactive Tapsafe.
2. Use the right temperature water. Allow your water to reach room temperature for coldwater aquariums, or heat it to match the temperature of the tank for tropical setups.
3. Don’t overfill your aquarium. Never fill an aquarium past the maximum fill line indicated on either your aquarium or filter.

For more information please read our testing & water treatment FAQs.