If you own a home tank, chances are you will want to do everything in your power to optimize its conditions. To make sure their fish can enjoy the best their tank has to offer, some aquarists have considered switching from normal water to RO water.

So, what is RO water? What are the advantages of using RO water for your freshwater aquariums? And what should you do when it comes to preparing RO water for freshwater aquarium? The answers to these questions will be addressed below!

What Is RO Water?

RO water is water that has gone through a process called reverse osmosis. Essentially, reverse osmosis is all about diluting a strong solution by letting it pass through a membrane.

Here, most of the molecules are small enough not to get stuck. But if the solution contains waste of any kind, said waste will be separated by the filter.

As a result, the water that passes through the membrane is considered pristine and clean, as it does not have any pollutants or harmful chemical substances. What is left on the other side of the filter is called wastewater due to its toxic buildup.

RO water vs dirty water

Benefits Of Using RO Water In Freshwater Aquarium

Now that you have understood what RO water is, let’s learn a bit more about its role when placed inside an aquarium. Granted, RO water is much fresher and cleaner than typical water.

But does it bring about any benefit for your fish?

Unsurprisingly, yes! First of all, RO water is highly pure. As mentioned above, it does not contain waste or any toxins. Thus, it will not be a threat to the well-being of your fish, especially species that take a liking to high-quality water environments.

Secondly, RO water has a neutral pH of 7. This gives you the flexibility to adjust the pH levels based on the needs and preferences of your community tank.

Unlike typical water where the pH level fluctuates wildly, RO water provides you with a stable benchmark so that you know what to expect when monitoring the tank’s conditions.

Last but not least, RO water is 100% safe from chemicals. Since all heavy metals and harmful toxins such as chlorine and nitrate are removed beforehand, you can leave RO water on its own and pay attention to other factors in your tank.

[display-posts id=”4880″ image_size=”thumbnail” posts_per_page=”1″]

Preparing RO Water For Freshwater Aquarium – Guidelines

Preparing RO water for a freshwater aquarium is not a big deal. Below are two different approaches when it comes to RO water preparation.

Easy RO water

The easiest way to prepare RO water is to mix it with tap water. You can easily get RO water at the store as a sample. Then, proceed to stir these two types of water and wait for a few minutes. Voila, you are done!

However, it should be noted that mixing RO water with tap water does not guarantee RO water in the end. For example, if the alkalinity level in tap water is too high, the RO water’s effect will be neutralized.

Or, if the tap water is too polluted, finding the right ratio so that RO water can balance out the heavy metals is tricky.

Hard RO water

If you want to ensure the quality of your RO water, preparing it the hard way is required. Here, you will have to add the minerals back inside the water through commercial chemical products. These items are designed specifically to replicate RO water, so you should be fine as long as you follow the instructions carefully.

After adding the chemicals, check the pH level and see whether it has achieved a neutral state. If not, make sure to continue adjusting the input of chemical substances until a pH level of 7 is achieved.

Next up, pay attention to the alkalinity level. If it is too high or too low, it can negatively affect the pH level. After ensuring that all parameters are in check, you can proceed to introduce your fish to the water.

RO water cleaning filter

[display-posts id=”4447″ image_size=”thumbnail” posts_per_page=”1″]


1. Can I use RO water for freshwater aquarium?

Yes. While it is not a must, having RO water for freshwater aquariums can bring about immense benefits for your fish. Not only is it cleaner and fresher, but it also helps regulate the environment inside the fish tank.

Again, while using RO water for a freshwater aquarium is highly recommended, feel free to leave out this advice if you think it is not suitable.

After all, RO water is expensive. And once your fish get a taste of what it feels like to live in a RO water-filled tank, they will raise their standards and not accept normal water.

2. What should I add to RO water for the aquarium?

When preparing RO water for aquariums, you must remineralize it beforehand. This means that you have to put in baking soda, a bit of calcium chloride, and Epsom salt. Or, you can consider using remineralizing cartridges to save time.

[display-posts id=”3624″ image_size=”thumbnail” posts_per_page=”1″]

3. Can I mix RO water with tap water for the aquarium?

tap water

Yes. If done correctly, mixing RO water with tap water can create the ideal water for your tank. However, there is no guarantee that it will work in all cases.

Therefore, you should stick to normal water or RO water on its own when preparing your aquarium. Trying too hard may cause your fish to suffer from the wrong water conditions.


Preparing RO water for a freshwater aquarium is no easy task. But as long as you get the hang of this procedure, replicating it will be a piece of cake.

And, of course, if you find these tips and tricks helpful, do not forget to share them with your friends and families!

Alex is a pet freelance writer and editor with more than 10 years of experience. He attended Colorado State University, where he earned a Bachelor’s degree in Biology, which was where he first got some experience in animal nutrition. After graduating from University, Alex began sharing his knowledge as a freelance writer specializing in pets.

Comments are closed.