Can You Use Hot Tap Water for Fish Tank?

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Setting up your first tank involves many uncertainties. What fish to get, how and what to feed them, what water conditions do they require, etc.? All these questions may seem overwhelming for a novice fish keeper, but they do require answers before any significant engagement.

Today, we will discuss aquarium water conditions and how to create the ideal living environment for your fish.

What is the Best Water Temperature for Fish?

The answer depends solely on the species that the fish belongs to. Guppies, for instance, thrive in water temperatures between 72 to 82 °F, but there are other fish species with a larger temperature range. The fancy goldfish qualifies here, with preferred temperatures between 55 to 80 °F.

The white cloud mountain minnow goes even lower than that, with acceptable temperatures between 40 to 80 °F.

These are all adaptable fish species capable of withstanding impressive temperature swings. Guppies themselves can cope with temperatures as low as 64 F if the situation requires it.

That being said, you should always monitor the water’s temperature to make sure it stays within the acceptable parameters. Wild temperature variations will hurt your fish, no matter how adaptable they are.

Excessively cold waters will affect the fish’s immune system, while hotter environments will lower the water oxygen. The latter will cause your fish significant discomfort and even lead to asphyxiation.

How Long Until Tap Water is Safe For Fish?

Ideally, you should allow tap water to breathe for 24 hours at a minimum before using it. Tap water contains excessive amounts of chlorine which sterilize it, making it safe for humans. The problem is that the same substance is deadly to your fish.

Chlorine acts as a poison and can prove lethal for most aquarium fish, even in moderate concentrations. You should always rely on a 24-hour window before introducing your fish to a tap water environment.

Furthermore, I recommend testing the water even after the 24 hours have passed. Check chlorine, ammonia, and nitrates levels to make sure that the environment is safe for your fish.

Is Kettle Water Safe for Tank Fish?

Yes, it is. There’s plenty of misinformation regarding this topic, unfortunately, stating that boiling the water will affect the water’s oxygen levels. This, in turn, will make boiling water unfit for fish since it will contain less oxygen than in its pre-boiled state.

All this is obviously false, and it’s really easy to tell why. Consider you have 5 gallons of water, boil it and cause 1 gallon to evaporate. You will be left with 4 gallons of water. This water has the same chemical composition as before boiling. It still contains 1 atom of Hydrogen and 2 atoms of oxygen; the only difference is that you have less water available. That’s it.

The boiling process doesn’t break the composition of water molecules into Hydrogen and Oxygen; it only separates molecules from one another.

The only process we know of that breaks H2O into H and O is the process of electrolysis, and that doesn’t involve boiling the water but electricity.

So, yes, Kettle water is safe for your fish. So long as you allow it to cool down before introducing the fish.

How To Heat Up Fish Tank Water Quickly?

The optimal method would be to use a water heater. It’s effective, safe, and will allow you to control the water temperature better. If the heater is not an option, a homemade solution will do.

Just grab a plastic water bottle, fill it with hot water and place it in the tank. This method is less accurate than a heater, but it will get the job done. Just place the water bottle in the tank and let it float freely. You can occasionally verify the water’s temperature and remove the container once the temperature has reached the ideal parameters.

As a useful note, try to have the water in the bottle 40 degrees F hotter than the temperature you’re aiming for. So, if you want to set the tank’s temperature to 75 F, the bottled water should be around 115 F.

Can You Add Warm Water to the Betta Fish Tank?

I wouldn’t recommend it. The problem with adding warm water to your Betta tank is that you cannot control the dispersion. If you’re pouring warm water on one end of the tank, the flow of heat will disperse unevenly. This will cause Bettas to experience cold water in one part of the tank and warmer temperatures in another, which can cause them discomfort.

If you want to add warm water into the Betta tank, here are some useful suggestions:

  • Always check the water’s temperature – You don’t want the water to be too hot. Check the temperature and make sure that the warm water is only several degrees hotter than tank water. You can also pour it in stages, each time heating up the water slightly more than last time. This will help you increase the tank’s temperature gradually to reduce the temperature shock.
  • Distribute the water evenly – Instead of pouring the water on one end of the tank, spread it across the water’s surface. This will allow for more even distribution and will heat up the entire tank water faster.
  • Try not to remove the fish before the procedure – I know you might want to adopt the safest strategy, but removing the fish before adding the warmer water may do more harm than good. The moving process may stress your Bettas unnecessarily and could even hurt them.

Can You Clean Your Fish Tank with Hot Water?

Yes, you can. Using hot water to clean your tank is actually better since hot water is more effective at removing algae and dirt.

Just make sure to avoid using hot water when cleaning the filter. This could kill off the cultures of beneficial bacteria populating the device.


Tap water is completely safe for your fish, so long as you treat it before adding it to the tank. You can either collect it and wait for the chlorine to dissipate naturally, or boil it, accelerating the process. If you don’t want to wait for so long, you can use a dechlorinator, which will make tap water safe for your fish.

Whatever you do, I recommend testing the water’s parameters before adding it to the tank. Check the ammonia, chloramines, and nitrates levels, and verify its temperature to make sure it’s safe for your fish.

You can then heat it up according to your needs and pour it into the tank using my suggested methods.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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