5 Best Reverse Osmosis (RO/DI) System for Aquariums

A reverse osmosis system functions as a filter in aquarium setups. It extracts all contaminants from tap or well water, creating purified water for your aquarium fish.

New technologies have boosted the systems’ capability, and models on the market can remove as much as 99% of impurities.

Reverse osmosis systems are especially popular with saltwater aquariums because RO/DI water can greatly reduce the algae growth, but it can be used in freshwater shrimp tanks as well in freshwater aquariums.

You can find reverse osmosis water in most aquarium shops, but it can be costly to buy the water every time you need it. A reverse osmosis system is an excellent investment in the long run.

Best Reverse Osmosis Systems for Aquariums

Best Reverse Osmosis (RO/DI) System for Aquariums

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Best Reverse Osmosis (RO/DI) System for Aquariums

Below you can find my reviews of the top reverse osmosis system I recommend for aquarium owners.

1. AquaFX Barracuda 100 GPD RO/DI System

This model fits both saltwater and freshwater setups, which is convenient because you no longer have to buy a different model for different aquariums. It is powerful, and you will get value for your investment.

This 4-stage model features a carbon block filter, deionizing resin filter, reverse osmosis membrane, and a sediment filter. These impressive features will remove all the pollutants from your tank and give you peace of mind.

The AquaFX Barracuda 100 is built to be both functional and durable. A pressure gauge will make it impossible to exceed the suitable pressure for filtration. There are solid aluminum brackets to eliminate the problem of rust.

It also has a clear filter housing which will make filter changes easy and efficient. The filter wrench and the quick connect fittings will make installation easy.

The system has a high-flow membrane so that you get a high speed of filtration. Even with the fast speed filtration, AquaFX has still equipped the system with a high rejection membrane to remove dirt and contaminants.

The model, however, has been reviewed to have a high-water wastage ratio.


2. Aquatic Life RO Buddie Reverse Osmotic Systems

The winning feature with this model is its compact design. At 13.8×7.5×6 inches, it will easily fit in small spaces.

One of the impressive fittings of the system is the RO Buddie TFC membrane, which is designed to remove all the harmful elements in water. The membrane works with Carbon and Sediment pre-filter cartridges to remove heavy metals, particulate matter, chlorite, and total dissolved solids.

This 3-stage model can be easily upgraded to a 4-stage system by adding a Deionization cartridge from the Aquatic Life brand. You, therefore, do not have to buy another RO system when you want more functionality.

The Carbon and Sediment Cartridges are up-front in addition to being easy to replace. The faucet adapter makes it effortless to link to a standard male hose thread. The model also includes a filter wrench, mounting brackets, and membrane. It also has a kit for drinking water in case you decide to use the system to purify your drinking water as well.

Be careful when fitting this model, as it can leak if installed improperly.


3. Liqua 5-Stage Reverse Osmosis and Deionization RO/DI

This model is designed to suit multiple applications, including aquariums and laboratory testing. As long as you want ultra-pure water, this system will fit your needs. It comes pre-assembled to make installation hassle-free.

The 5-stage filtration is guaranteed to result in pure and contaminant-free water. The polypropylene sediment filter will extract all the particles in the water before it gets to the membrane.

The filter is replaceable, and it is more convenient to remove instead of removing the membrane. The filter removes any materials that can clog the membrane like minerals and dust.

Two activated carbon cartridges eliminate volatile organic elements, in addition to chloramine, chlorine, and radon. Your marine pets will thrive in the clean water that is guaranteed by this model.

The RO membrane, in turn, removes heavy metals, mineral salts, arsenic, and lead. The deionization cartridges will get rid of any traces of nitrates, ammonia, phosphate, and metals.

The model is packaged with a filter wrench, an automatic shut off valve, a manual flash kit, and all the necessary fittings for installation.


4. Koolermax AR-122 6-stage RO+DI Aquarium Reef RO System 80 to 120 GPD

This model is designed to fulfill the needs of reef tanks, thanks to its high-power filtration system and the GDP range of 80 to 120. Its 6-stage filtration includes a reverse osmosis membrane, two deionizing resin filters, and a sediment filter.

There are two kinds of carbon block filters to get rid of 100% of the chlorine. All these filtration media ensure you end up with clean and clear water.

The 120-gallon capacity is particularly ideal for large tanks. Additional features include a pressure gauge, tubing, auto shut-off valve. Koolermax offers free tech support on installation, which is an attractive incentive.

You can read the operating pressure on the pressure gauge and know when the bottom three filters need replacement.

This model has made improvements to reduce the wastage ratio, which was a concern with previous models. You can expect little water wastage when cleaning. It is also easier to maintain your aquarium’s PH because of the additional DI filter.

This model’s functionality and power make it perfect for reef aquarists.


5. Geekpure 3-Stage Portable Aquarium – Countertop Reverse Osmosis Water Filter System- 100GPD

This highly-efficient system will remove over 1000 contaminants and 99% of heavy metals, chlorine, arsenic, fluoride, mercury, and odors.

The model is durable and solid, and all its tubing and fittings comply with NSF/ANSI standard 58. The RO unit measures 14.8 × 9.2 ×3.2 inches, and it can easily fit into small areas.

The 3-stage filtration system includes a PP spun filter, which extracts sediments, dirt, and sand. The carbon filter removes tastes & odors, chlorine, and very fine particulates. It also has a TFC Ro membrane that gets rid of iron, heavy metals, fluoride, and lead.

You can use the lead-free faucet if you also want to use the system for drinking water. The seven replacement filters will keep your model running for as long as two years. The instructions are also easy to understand, which eliminates the costs for professional installation.


How RO/DI System Works?

RO/DI stands for Reverse Osmosis Deionization while RO is for Reverse Osmosis system. Some RO systems will have an additional DI stage of filtration to filter water down to ZERO Total Dissolved Solids (TDS).

RO systems typically suit freshwater aquarium setups. An RO/DI system is necessary for marine aquariums when mixing saltwater and topping up with freshwater because of evaporation.

Most standard RO systems will make use of four filtration stages to purify water. If the supply water is densely polluted or the RO/DI system is used a lot, it is better to invest in a 5- or 6-stage system which comes with an extra DI stage or carbon included.

The system works as follows:

Input Stage

The input water is first channeled into the RO/DI system. The input can be done via a garden hose adaptor that directly links to the threads of a garden hose.

Faucet adaptors can also be used to either connect to the household faucet or the plumbing underneath sinks. Cold water is better because hot water will damage the system.

Sediment Filter

This filter performs mechanical filtration by trapping the sizeable particles of dirt, debris, and pollutants.

These particles will clog up the filter over time and should be replaced every six to eight months or when they become inefficient.

Carbon Filter

The carbon filter is typically fortified with granulated carbon to catch organics and elements like chloramines and chlorine.

Chloramines will quickly exhaust your carbon filter, and you should consider a 5- or 6-stage system if your input water is heavily polluted.

Most aquarists will change the carbon and sediment filters together after 6 to 8 months. The advantage of changing the filters regularly is that the RO membrane will be protected from contaminants that may escape inefficient filters.

RO Membrane

This is the most vital part of any RO/DI system. The water will be filtered via several layers of thin film to extract up to 98% of pollutants like heavy metals, salts, and bacteria.

It is monitored with pressure gauges and/or TDS meters.

Water from the membrane will be divided into the product water channel and the wastewater line.

The latter features a flow restrictor, although you can bypass this with a flush valve kit and flush the membrane free of particulates both before and after use.

The wastewater will accumulate in a chamber for alternate uses like washing your car or spraying into your lawn.

The system gives out one gallon of pure water for every three gallons of wastewater. The wastewater can add up quickly if you have a large aquarium, which is why you need to find alternate uses for it.

The water leaving the membrane will be nearly pure, and most models have an additional stage to get rid of any traces left.

Deionization Cartridge

This stage has positive and negative charged resins that remove leftover traces of pollutants like phosphate, silicate, and nitrates. 6-stage systems will employ two deionization cartridges, and you can be sure no contaminates will leave the system.

The functionality of the RO/DI system is boosted by the use of pressure gauges and TDS monitors.

The pressure gauge evaluates the water pressure flowing into the membrane. The recommended level of water pressure is between 40 to 80 PSI.

If your model’s pressure is in this range, you can be sure your system is performing optimally. If the pressure is below 40 PSI, you can replace the carbon and sediment filters or invest in a booster pump.

The TDS monitor uses inline probes to calculate the total dissolved solids, and it can be used to know when to replace the membrane or the DI cartridge.

Why Use a Reverse Osmosis System? Is it Necessary?

Many aquarists rely on reverse osmosis to remove impurities in aquarium water. The system will fit anyone looking to get rid of many kinds of impurities and ions and create a healthy environment for their pets.

It is not recommended to use the water you get from your municipal water supply for your aquarium. The mineral concentrations and PH vary from region to region, and there can be amounts of harmful elements like nitrates and phosphates.

If you live in a jurisdiction with hard tap water, for example, you risk exposing soft water fish to an inappropriate environment.

Other areas will fortify their water with phosphate and its elements to deal with pipe corrosion, and this will minerals will encourage algal-growth in your setup.

Metals like lead and copper commonly leach into water supplies from metal plumbing.

You may be wondering why you need a reverse osmosis system if your aquarium already has a filter. Most people, especially beginner aquarists, select the wrong kind of filter for their setups.

The choice of a filter needs extensive knowledge of the kind of aquatic pets you intend to keep and the environment you want to maintain. A reverse osmosis system, on the other hand, fits reef, freshwater, and marine aquariums.

When compared to tap water, reverse osmosis water will provide many benefits for your fish tank. It is low in contaminants, which promote the growth of algae.

You can keep a range of marine residents in reverse osmosis water, while your tap water will only sustain a limited variety of fish.

Benefits of Reverse Osmosis Filtration

Below are more benefits of using a reverse osmosis filtration system and RO water for your aquarium water changes.

Eliminating the Need for Cleaning Filters and Purification Chemicals

Some aquarists rely on chemicals and filters to filter out pollutants from their tap water. Not only is this method costly, but it is not very effective.

These solutions cannot extract chloramine compounds and chlorine, which pose a great threat to the water quality of any aquarium.

Reverse osmosis systems will remove particles and harmful compounds like phosphates, silicates, nitrates, and chlorine.

Creating a Stable Environment for your Fish

Most fish species demand stable conditions of PH, temperature, salinity, and other factors. Your pets will likely get stressed if they are drastic adjustments in your aquarium, and they will become vulnerable to diseases.

You can employ remineralization to adjust reverse osmosis water to fit your setup. A reverse osmosis system is easily configured to produce the appropriate water parameters for any aquarium.

Units are Easy to Install and Use

Most brands sell pre-installed reverse osmosis systems to make them user-friendly. The Liqua 5-Stage Reverse Osmosis and Deionization RO/DI, for example, needs little-effort to get it running.

Brands like Geekpure sell their models with easy instructions, making installation hassle-free. You only need to spot a location with a source of water and a drain.

How to Choose an RO/DI System for Your Aquarium?

Technological upgrades have improved the functionality of reverse osmosis systems, and knowing the features available will help you select an ideal one.

How Many GDP (Gallons Per Day) Do I Need?

The GDP rating will describe the power level of a model. It describes the maximum number of gallons of pure water produced by the system per day. It is an estimate because it only calculates the level of water produced if the model functions at maximum pressure. Most taps will, therefore, produce around 60 to 85% of the rated GDP.

The calculations are typically tested with 77 °F water parameters and 60 PSI, which will often be different from the environment of your aquarium.

The amount of purified water you require for your setup depends on how often you flush the water, the size of the tank, and whether the system is linked to a storage tank.

If you can store the additional purified water, get a system with a higher GDP rating because you will have pure water on-demand basis.

You can also use your absolute minimum GDP to determine the power you need in a system. Divide the capacity of your aquarium in gallons by the days between when you do a water change to get the absolute minimum GDP.

Filtration Stages

The systems are commonly available in three-, four-, or six-stage filtration levels.

Some models can feature two stages of the same filtration, like the Koolermax AR-122 6-stage RO+DI Aquarium Reef RO System with two carbon filters.

The more stages a model has, the more complex and bigger it is. Three-stage models are generally light-weight and compact, making it easy to fit them under aquariums and in small cabinets. A four-stage system is more efficient, thanks to the deionization stage added after the water passes the RO membrane.

The six-stage models are the most-efficient and will suit larger setups. The additional carbon filters extract volatile organic compounds, chlorine, odors, and any cloudiness.

The system you get should fulfill the needs of your tank. A six-stage model, for example, maintains the stable environment and water quality necessary in a reef tank.

Waste Water Production

Reverse osmosis systems typically produce more wastewater than pure water. If you live in a region with limited water resources, consider the wastewater produced by a model to reduce water wastage.

Type of Membrane

The RO is the most essential, as well as the most expensive part of your system. It traps dissolved solids, and three-stage models will typically have it as the last process.

If you are using fairly pure input water, you can use Cellulose triacetate membranes as their removal rates range between 88 to 94%.

Thin-film composite (TFC) membranes extract 94 to 98% of dissolved solids, which makes them very popular. They are typically fitted in six-stage models because they can be ruined by chlorine. These membranes are better suited for sensitive aquariums.

How Often Should You Change RO/DI Membrane?

TDS meters are commonly used to determine how well the RO membrane is functioning. A membrane working under optimal conditions should not produce water that is at less than 95% quality.

Membranes can last for several years, although they are quite prone to damage. It is advisable only to use cold water for reverse osmosis systems as hot water will ruin the membrane.

The quality of the RO membrane is also informed by the efficiency of the sediment and carbon filters. Any particulates that escape these filters and get into the membrane will only compromise its functionality.

What does GDP Mean in Reverse Osmosis?

GPD in reverse osmosis describes the maximum gallons a system can produce in a day. The actual flow rate of any system, however, in GDP will depend on your household’s water pressure and temperature. If these parameters are low, you will get a lower GDP than the one rated for your machine.

Is a 3-Stage RO/DI System Enough for My Aquarium?

A 3-stage RO/DI system includes sediment and carbon filters, and an RO membrane. These layers of filtration will be enough if you get your water from a well and need a simple filtration system. If your water is from the municipal supply, however, or if your input water is heavily polluted, consider getting a more complex system.

How Much Water is Used Through Reverse Osmosis?

Reverse osmosis produces one gallon of pure water for every three gallons of wastewater. The wastewater may not be good for your aquariums, but it is safe for alternate uses like watering your plants and washing your car.

Why Do You Need to Remineralize Reverse Osmosis Water?

Reverse osmosis systems are non-selective in the way they function. In the process of removing pollutants, they also remove good compounds like magnesium and calcium, which are beneficial to aquariums.

Remineralizing involves the addition of useful minerals to reverse osmosis water. You can implement this process by adding an alkalization process to your RO system.

You can also add mineral-rich salts like Himalayan salts or using mineral drops. An alkaline water pitcher will also balance the PH of the tank water.


Reverse osmosis systems have the benefit of making your tap water safe for use in your fish tank. The water supply of your region will typically have traces of compounds like chlorine and chloramine, which promote algal-growth and impact on the health of your aquatic pets.

The PH and other water parameters of your local water supply also limit the kind of marine residents you can keep.

Reverse osmosis water is free of pollutants and impurities, thanks to the filtration layers it passes through. Models will either offer three-, four-, or six-stage filtration, depending on the system you have.

Remineralization will add beneficial elements like magnesium and calcium to encourage the health of your fish.

Questions and Answers

Frank Gross February 17, 2020 Reply

I’m new to the hobby. A R/O filter is meant to produce water to put in the aquarium, not filter the water already in an aquarium….. correct?

    Exactly! An RO system will remove almost all impurities from your tap water. Please note that you still need to add salts to the water, because fish can’t live in RO water.

      FRANK GROSS February 21, 2020 Reply

      We are looking at all scenarios. In terms of dedicated, R/O under sink drinking water systems as compared to mainly aquarium water R/O systems , does one “refine” the water better the the other? Will one give overall better results in a given application than the other or will both work equally well in either case? We would like to have drinking water.

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