How to Remineralize RO Water for Freshwater Aquarium?

Reverse osmosis (RO) removes or reduces several contaminants from tap water. The water contains negligible hardness or alkalinity, few dissolved particles, and near-neutral pH.

Even when tap water has excessive hardness or pH, we may give fish with lower pH values.

RO water is devoid of minerals and chemicals that might harm aquatic life, but it’s also could be unhealthy. Your fish tank essentially requires certain minerals and water conditions.

You may condition the water for your fish’s requirements by adding a combination of calcium chloride, Epsom salt, and baking soda. It is the ultimate method for creating a ‘tailored’ environment for your valuable aquatic life.

This article explains the procedures and precautions to remineralize RO water for a healthy freshwater aquarium.

Can I Use RO Water in Freshwater Aquarium?

Pure as crystal, RO has purified water to a superior standard. Because of its high purity, RO water is ideal for use in fish tanks.

Nothing in there should be harmful to your fish. There won’t be any chlorine, ammonia, nitrates, or trace elements.

Whether to use RO water is a personal choice; however, if you have a single community tank whose tap water supply is of high quality and low in nitrates and other contaminants, RO water is typically unnecessary, particularly if you select fish to suit the hardness and pH levels of the tap water.

Moreover, using RO water may be expensive and cumbersome, and once started, we must maintain it to keep the aquarium’s environment sustainable, therefore it should not be done casually.

Whenever the water’s pH and/or hardness must be lowered, when many tanks with varying temperature and pressure needs are kept, or when the water’s overall quality is poor, RO becomes very beneficial.

If you fulfill even one of these requirements, it is quite likely that you will require an RO system for your fish tank.

Is RO Water Good for Aquarium Plants?

In order for aquarium plants to have optimal growth conditions, it is essential to strike a balance between the many forms of nutrients that are necessary.

Because the water that comes out of the faucet at home includes several contaminants, achieving such a balance is, at best, challenging and, at worst, impossible.

The fundamental advantage of RO water for plants is that it provides a consistent supply of clean, purified water.

Reverse osmosis has the ability to remove any contaminants between 90 and 99.99%, including minerals and nutrients.

This not only simplifies the calculation of the mineral balance but also eliminates any potential conflict with fertilizers.

One significant downside of RO is that it removes even the good contaminants that are useful to plants.

To address this issue, we must remineralize the RO water.

Moreover, RO water is more expensive than distilled water, which is equally good and better than tap water or rainwater for aquarium plants.

What to Add to RO Water for Freshwater Aquarium?

One of the issues with RO water is that it does not contain any trace minerals. Magnesium, iodine, strontium, and molybdenum, as well as calcium, are a few examples of the essential trace elements that fish and invertebrates in an aquarium require.

Minerals are required by a diverse range of organisms, including fish, corals, shrimp, and snails.

Remineralization helps rectify these shortages of minerals in RO water. It is contingent upon the proportion of RO water that is being utilized as well as the parameters that are being retained.

Using a combination of calcium chloride, Epsom salt, and baking soda will do wonders for the health of your fish.

In order to get your tank ready for the remineralization procedure, you will need to rinse properly and wash it out first.

Before mixing it into the remineralized RO water, give it a thorough scrubbing with the tap water and then set it aside to dry.

Mixing Tap and RO Water for Aquarium

Blending a certain amount of RO water with tap water in order to get the desired pH level and hardness of the water.

It is the easiest way to utilize RO water to soften the water and lower the pH level. This method of lowering gH (general hardness) is relatively simple.

The amount of gH that is produced as a consequence of mixing equal parts tap water and RO water is equivalent to one-half of the original quantity.

If the gH of the tap water is 20, but the fish tank requires a gH of just 5, then mixing RO water with tap water will produce the needed result.

Obtaining a lower pH value by combining tap water and RO is a bit more challenging since the kH (carbonate hardness) value must also be taken into account, and because pH (percentage hydrogen) values are logarithmic, combining half RO and half tap water will not result in a halving of the pH.

In most cases, the simplest method to go with this issue is to use trial and error with various mix ratios and to perform regular testing.

Nevertheless, you should not add any of your blends to the tank until you are certain that you have achieved a stable pH level.

Storing RO Water for Aquarium

Determining how much water your fish tank needs is the main issue when designing a stored water system.

This depends on the size of your aquariums and how much water you want on hand without refilling.

After determining how much water you need, you must consider space and how to move it where it needs to be. Based on your specific requirements, the storage containers you select will vary.

Some may be happy with a plastic barrel, while others may need large tanks.

Plastic, stainless steel, or other materials approved for use with food should be used for storage tanks.

Never put anything back into a container that has held hazardous substances like gasoline, paint, or insecticides.

Avoid putting anything in your fish tank that you wouldn’t want to seep into your water.

How Long Can You Store RO Water for Aquarium?

Depending on the container that you use for storage, as long as you maintain the RO water aerated, cold, and dark, you should be good to go for a few months.

This is due to the fact that the container used to store RO water may, over the course of time, leak metals or artificial nutrients into the water.

In addition to that, there are some instances in which the filter will let fungus or algae pass through without being prevented.

Nevertheless, a UV test is something that must be taken into consideration.

It is possible to keep outdoor ornamental ponds clean using a variety of approaches, which enables these ponds to treat a substantial amount of water and prevent the spread of harmful bacteria.


RO water is too soft and lacks any significant hardness to be used in an aquarium without the addition of helpful minerals.

Without these key components, the pH becomes very unpredictable, which might provide unexpected test results.

A remineralizing buffer may fix this problem easily; as there are options for both fresh and saltwater use, so the fish keeper can create the ideal conditions for any species.

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