How to Remineralize RO (Reverse Osmosis) Water for Freshwater Aquarium

RO water is a type of water free of other substances, only H2O and nothing else dissolved. It is the purest presentation of water, allowing the aquarist to have complete control of the chemical parameters of the water that will be added to the aquarium.

       It turns out that some animals need a more profound treatment than simply using a water conditioner. These animals do best in environments whose water is appropriately controlled, containing only the specific content of minerals they need to survive.

       The water from the RO alone should not be used directly in the freshwater aquarium, as it has a very low, close to neutral, content of elements and minerals. The water to be used must always be remineralized.

       Adding salts takes place through the remineralization of this RO water; we use specially developed products, easily found in aquarium stores.

What is Reverse Osmosis

       Reverse Osmosis, commonly called RO, is a process where you demineralize water through membranes.

       When water is pushed under tremendous pressure through a semipermeable membrane, the process occurs. The membrane only allows the passage of water molecules and prevents the passage of larger molecules such as minerals, organic matter, contaminants, microorganisms, and any chemical or salt.

       RO water is nothing more than the water purification process that many marine and freshwater fish farmers use to protect their species from harmful chemicals and particles in the water and be in complete control of the chemical properties of their tank waters.

       There are limitations to using RO water. The main disadvantage of using this type of water in an aquarium is that it is very pure. That is to say, RO water does not have any minerals that can help support fish or balance the water stability.

Benefits of using RO water

       The water that comes from the distribution center contains a variety of contaminants, including chlorine, bacteria, and viruses, in addition to not being able to specify its chemical composition.

       When purifying water with RO systems, you have the security of knowing that the water is free of contaminants and solids; having pure water, you don’t have to worry about doing dozens of tests and adding different products to stabilize it in the necessary parameters for your fish or invertebrates.

       As stated before, the reverse osmosis filter produces high purity water, free from salts that interfere with the water hardness, chemicals such as chlorine and fluor, and microorganisms. This provides an entirely neutral environment for you to create the ideal conditions for your tank’s inhabitants to thrive.

Why remineralize RO water?

       It is important to remember that because it is pure, this water will not have minerals and elements necessary to the health and well-being of the fish or invertebrates kept in the aquarium, and the water’s ability to maintain the proper stability; as well as for plant growth. Therefore, it is always necessary to add elements and minerals to it so that animals can grow and develop.

       Reverse osmosis is a non-selective process in removing ions through membranes; that is, its stages will remove absolutely all the components of the water. This sterile water has harmful effects on animals, especially aquatic animals.

       Trace elements present in water help fish thrive. Furthermore, as fish have semipermeable membranes, they can experience deadly trauma in pure water from RO. Minerals related to magnesium and calcium are responsible for acting as a buffering effect, stabilizing the pH and water hardness; because of this, RO water is volatile, quickly fluctuating its parameters.

Remineralizing RO water

       As mentioned before, because the RO system removes elements necessary for life, we must remineralize the water before introducing it into our tank. Fortunately, reintroducing these minerals into the water is a simple task.

       RO water remineralization should be done concerning your aquarium type and inhabitants. For example, if you have an African cichlid aquarium, you will remineralize the deionized water with some salt suitable for African cichlids. Who has a planted aquarium will use products that favor the growth and development of plants. Those who have shrimp will use products that mimic the conditions of the shrimp come from. And so on.

Trace elements and minerals

       Using RO water will have several benefits in your aquarium. Using purified water will ensure that you will not add any unwanted elements to your aquarium. Still, you will have to control and dose the proper minerals for fish, invertebrates, and plants through products sold in aquarium stores.

       Aquarium-grade remineralizers are the safest and most efficient choice to make. They are products that contain all the trace elements and minerals necessary for the correct functioning of your aquarium and fish.

       You will find several product options in retail stores, including precise labels. We find trace elements suitable for shrimp, discus fish, soft water fish, hard water fish, etc.

       Remineralizers are generally found in the solid form (usually in powder form) and the liquid state; some solids require water preparation and settling before being added. Liquid remineralizers can be mixed with water and immediately added to the tank.

Remineralizing Filters

       This case is not ideal for freshwater aquariums, but it can be used. There are water remineralization filters suitable for RO systems.

       These filters add a specific amount of minerals to the RO water. Alternatively, you can use an alkaline water filter, buffering the water and removing its susceptibility to sudden changes in pH.

       This type of remineralizer should be used with caution and is best suited for community aquariums with more resistant fish and water tending to the alkaline side of the scale. Anyway, even using this filter, it is recommended to add trace elements.


       Reverse osmosis is the most effective type of water purification, removing over 99.9% of the total dissolved solids from unfiltered water. If you try to find the cleanest, purest water, you will get it with reverse osmosis.

       In freshwater aquariums, its use has been growing mainly among those who keep fish in waters with a specific parameter or those who have poor quality water provided by the supply network. You must be familiar with all the features of an RO water treatment before deciding to use this type of water.

       Due to the ease of use of remineralizers on the market, the remineralization technique is accurate and flawless. Regardless of the water chemistry you want or whether your tap water comes in full of nitrogen and phosphates, RO water is the perfect solution for any aquarist.

       Avoid homemade techniques such as introducing Himalayan salt and the use of DIY minerals. However, they present some elements functionally, they will not be in the correct amounts or proportions, and the raw material used is not ideal.


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