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Reverse Osmosis systems -sometimes referred to as RO/DI systems (Reverse Osmosis-Deionization) are advanced filters that are used to remove impurities from tap water such as sediment, chlorine, phosphates and heavy metals. RO/DI filtration systems are mostly important for saltwater aquariums because even trace amounts of these elements can build up over time and lead to algae growth or other imbalances in saltwater tanks that can be fatal to your fish and corals.

Many aquarium suppliers sell reverse osmosis water to use in your tank, but it can be difficult to run to the store whenever you run into a situation where you need to top off your tank. The costs of purchasing your water from the store on an as-needed basis can also be costly in the long run. The benefits of having your own RO/DI system can make it a great investment of both money and time.

It is also a good idea to have your own reverse osmosis system in place for security and peace of mind in the event of a leak or other unexpected problem where you can’t get to your supplier. RO/DI systems are different from other filtration systems as they are able to provide the most comprehensive filtration, removing over 95% of all contaminants. If you have never used a RO/DI system before, it might be a good idea to get a basic understanding of how they work.

How RO/DI systems Work

RO/DI filter systems can be boiled down to two main parts, kept in separate chambers for multi-step filtration. The first component is a reverse osmosis membrane, usually a polymer sheet, which filters the tap water on a molecular level. This is great for filtering out compounds that are bigger than a water molecule, but the filtration does not stop here. For the second step of the process, water passes through a deionizing resin which attracts any leftover charged particles that might be mixed in with the water.

Many RO/DI systems have a few extra features that help these two filters function at their best capacity. Sediment filters are often a part of these systems as a first-pass effort that cleans up any larger sediment particles from the tap water before it even gets to the fine-tuned filtration of the RO/DI. This takes some of the heavy lifting off of the finer filter membranes and is a pretty food first pass to clean up some of the larger impurities that can be found in tap water. Many RO/DI systems also feature a carbon filter of some kind. The activated carbon in these filters is great for breaking down chlorine and chloramine before it even gets to the reverse osmosis membrane.

Buyer’s Guide to Finding the Best Aquarium RO/DI System

There are many great options for RO/DI systems on the market today, so knowing what features to look for can be extremely helpful in sorting out the best fit for your aquarium set up.

GPD: Gallons per day, or GPD, is a common rating for reverse osmosis membranes and gives you some idea of the power level behind the filter in question. It is an estimate of the number of gallons of clean water produced by the membrane per day, and it is important to remember that it’s just an estimate. These numbers are usually tested with 77 degree water conditions and 60 pounds per square inch (PSI) – which might be very different from the conditions in your own setup. Use it as a guideline to compare filter models rather than a rule for how it will function in your own aquarium.

Automatic Shut-off Valve, or ASOV: Some filters with this feature will automatically stop the flow of water if the system is closed.

Stages: Each filter system will have a different number of stages of filtration, with more complex systems featuring multiple stages. Each stage will typically be a different method of filtration, so you can expect systems with more stages to provide a more thorough filtering.

Waste water production: It is also important to consider the waste water production of your filtration system. The amount of water used to operate the filtration system is not equal to the clean water output from the filter. Therefore, if you are in a drought-prone area or are otherwise limited in your use of water, it is important to look for a system that wastes as little water as possible.

Consider what you want to use the filter for. Many RO/DI models used by aquarists are also used by people who use it to improve their drinking water. Therefore, some of the models you will find come with extra parts and add-ons to integrate the system into their sink. If this is something that interests you, you might be looking for an all inclusive system. If you are planning on using this filter for your aquarium only, then you can probably find a more affordable option.

Now that we have a better idea of what to look for in a RO/DI system, let’s take a look at a few different models on the market. There are limitless options when it comes to RO/DI filters, especially when you consider all of the combinations you can make when you create your own setup, but we are going to take a closer look at a great variety of options.

Top 6 Best Reverse Osmosis System for Aquariums

1. Aquatic Life RO Buddie Reverse Osmosis Systems

The Aquatic Life RO system is available in three models: a 50-gallon four-stage, a 50-gallon three-stage, and a 100-gallon three-stage option. All three models feature a small footprint starting at 13.8 x 7.5x 6 inches, so they are unobtrusive and can be fit into smaller spaces. The 3 stage models feature reverse osmosis, sediment, and carbon filter. Here you can find the Aquatic Life RO Buddie Reverse Osmosis Systems.


  • An affordable option that comes in three models for your needs, one four-stage option
  • A smaller system is easy to install and store
  • Optional add on for drinking water


  • Not suitable for use in areas with high sediment levels

The four-stage system includes an additional deionizing resin cartridge. All systems use a thin-film composite membrane and come with a faucet adapter, mounting brackets, and membrane wrench. Additionally, this system has an add-on kit for drinking water including a pressurized tank and faucet- in case you would like to use your system for drinking water as well. It is worth noting that this brand does mention that New York City dwellers will require extra filtration, as the city water might have extra sediment levels that might be a little too much for this system to handle alone.

2. Express Water Reverse Osmosis Water Filtration System

The Express Water Reverse Osmosis Water Filtration is a high-quality 50 GPD five-stage system that is fully customizable to your water purification needs and is marketed toward filtering drinking water. Out of the box comes with five filters: a sediment filter, two types of carbon filters, the RO membrane filter, and an additional activated carbon finishing filter. Here you can find the Express Water Reverse Osmosis Water Filtration System!


  • A customizable system that can be upgraded or changed at any time without having to invest in a new system
  • Complete set up including faucet for drinking water and large reserve tank
  • 5 stages of filtration out of the box, with options for further filters


  • Deionization filter not included

The unique thing about this system is that you can swap out different types of filters as your water filter needs to change- for example if you move somewhere with a different quality water supply- so it is a long-term investment. The deionization filter cartridge is sold separately, which might be annoying for aquarists, but there are other specified filters that are compatible with this unit, including ultraviolet, UV, and PH stabilizers. It comes with all the parts that you will need to install, including adapters for many types of fixtures, and a 4-gallon reserve tank with an automatic shutoff valve to prevent leaks. Although this product has a vast array of features, it does not require professional installation and the Express technical help team is easily reachable to resolve any problems.

3. The Aqua FX Barracuda filter

The Aqua FX Barracuda system is a high-powered filter that comes in both a 50 and a 100 GPD model. This model is designed for aquarists right out of the box with the four-stage filtration system, which features a sediment filter, carbon block filter, reverse osmosis membrane, and deionizing resin filter. Here you can find the Aqua FX Barracuda System.


  • A powerful system can process up to 100 GPD- great for large aquariums
  • Four-stage filtration includes deionization resin filter


  • Does not come with replacement filters or customizable options

It has a built-in pressure gauge for measuring your PSI, rust-resistant aluminum installation brackets, and clear filter housing to make filter changes as easy as possible. The set also comes with quick connect fittings and a filter wrench to make installation fast and simple.

Out of the box, this model has everything you need for complete RO/DI filtration and the 100 GPD model provides enough power to cycle through more water in less time.

4. Geekpure 5 stage Reverse Osmosis system

The Geekpure Reverse Osmosis system is designed with drinking water in mind and features five levels of filtration: a sediment filter, a granular carbon filter, a carbon block filter, a reverse osmosis membrane, and a post-carbon filter. Here you can find the Geekpure Reverse Osmosis System!


  • The full filtration system includes attachments for drinking water
  • The higher power system is 75 GPD


  • Since this system is designed for drinking water, there is no option for deionization filtration

The storage tank holds 2.8 gallons, which is smaller than others we have seen and would fit nicely under a sink or in a room with size constraints. All brackets, tubing, and fittings required for self-installation come with this unit. It also comes with a certified lead-free drinking water faucet that can be installed in any existing sink or countertop. It also comes with 7 replacement filters, which are estimated to keep your system running well for 2 years.

5. Koolermax AR-122 6-stage RO+DI Aquarium Reef RO system

The Koolermax AR-122 system is designed specifically with reef tanks in mind. It is a high-power filtration system with a GPD range of 80-120 depending on your water pressure. The five-stage filtration system includes a sediment filter, 2 types of carbon block filters to eliminate 100% of chlorine traces, a reverse osmosis membrane, and two deionizing resin filters. Here you can find the Koolermax AR-122 System!


  • High GPD of 80-120 to produce more filtered water, fast
  • 6 stage filtration system offers fine-tuned filtration
  • Reasonably priced for the power and coverage


  • More limited customization options compared to other models

This unit comes with a one-year warranty as well as reliable technical support for installation assistance. It comes with a pressure gauge as well as an automatic shut-off valve, so all of your bases will be covered right out of the box.

For all of its power and functionality, it is No products found., and is a great choice for a reef aquarist who just wants to get a RO/DI system up in place for their aquarium exclusively.

6. The LiquaGen 6-stage Reverse Osmosis and Deionization System

The LiquaGen RO/DI system is a powerful, pre-assembled option that has a high membrane capacity of 100 GPD. It features 6 stages of filtration that includes a sediment filter, 2 types of carbon filter, the reverse osmosis membrane, and two deionization filters. Here you can find the LiquaGen RO/DI System


  • Higher-end GPD of 100
  • 6 stage filtration system for a high-quality cleaning
  • The additional flush kit extends the life of the system
  • Pre-assembled for convenience


  • Our most expensive recommendation

It is a compact system measuring 16×16 inches, and can easily be stored away. It comes with an automatic shut-off valve, a filter wrench, a manual flush kit as well as all of the fittings, tubing, and brackets needed for easy installation.

More Information on Reverse Osmosis Systems

Why are RO/DI systems important?

It is clear that installing RO/DI systems involve a fair amount of investment, both of funds and installation time. It can be tempting to write off RO/DI systems as an unnecessary upgrade- especially when your water supply is relatively clean. However, just because your water has not caused any problems yet does not mean it is not affecting your aquarium. Tap water is often dosed with organic compounds to make it safer to drink, not to mention chemical cleaning agents and debris from the actual plumbing hardware. Even if you are using a water conditioner, or some other nutrient-infusing method to prepare your tap water, it is likely not enough for a delicate ecosystem to thrive. This is particularly true of reef tanks, where these trace chemicals can be fatal in corals and other invertebrates.

If you are having water problems, or your reef tank is failing to thrive, it is definitely worth investigating if your water quality is the culprit.

Are Reverse Osmosis systems necessary for freshwater aquariums?

Freshwater species are often less sensitive to the trace impurities in the tap water, to the extent that a RO system would likely be overkill. However, if the tap water that you have is very hard, or may have contaminants in it, a RO system would make a lot of sense. Some freshwater species, like Discus, prefer soft water and can benefit from a purification setup.

My new RO/DI system is not producing the GPD it predicted. What gives?

It is important to remember that the GPD of a reverse osmosis filter is affected by many different facets of your setup and water supply. The temperature of the water, the room temperature, and your water pressure can all cause the system to produce RO water more slowly. The quality of your water supply can also have an effect on your system, as many are tested with a certain quality level of water. The total dissolved solids (TDS) of your water is something you might want to look into as you try and update your system.

How often will I have to change the filters or the membrane in my RO/DI system?

All aquarium enthusiasts are aware that nothing in the world of fish keeping comes without some upkeep. The life of your RO/DI system will be much longer if you take the time to perform proper maintenance and replace your filters on a routine basis. The most common recommendation is to change your sediment, carbon, and deionization filters every two years. However that is far from a rule of thumb, as the rate at which your filter clog up could be much faster depending on several factors. If the TDS of your water is high to begin with, all of your filters will be extracting a much higher amount of particles from the water, so you can expect to change the filters much more often.

Instead of relying on a measure of time to check and replace your cartridges, we recommend that you change them based on the number of gallons of water that have passed through them. Your filters should be checked every 3,000 gallons or so.

As for the reverse osmosis membrane, you can periodically check how it is doing by measuring the TDS of your output water. An optimal RO membrane should not be producing water at less than 95% quality. If it dips lower than this, its time to check it out. Membranes can usually last a couple of years before needing replacement, but that does not make them any less prone to damage. Damage is likely to happen if the membrane is allowed to dry out, or if it has come into contact with very hot or freezing temperatures. Likewise, if one of your other filters hasn’t been changed in a while, there is a chance that some larger particles are going to get through to the membrane and potentially cause some damage.

As they say, an ounce of prevention is worth a pound of cure. It is always worth it to take the extra few minutes to check the status of your filter than it is to replace an entire system due to negligence.


After looking over all the information, it is always a better investment- of both money and time- to set up your own RO/DI system instead of constantly purchasing reverse osmosis water from your supplier. Although the initial money investment can be steep, the costs recoup very quickly, especially if you have a larger reef tank where the costs of outside water begin to add up. The added peace of mind of having your own steady supply of reverse osmosis water is also well worth the extra time of getting your own RO/DI system.

Now that you have a basic understanding of the components of RO/DI filtration, how it works, and what’s available on the market, you will be able to make the best choice for your situation. Although there is no way to identify the best system on the market, knowing what features are best for you will ensure a great fit. For aquarists on a budget, the No products found. have all of the essentials needed to get you up and running, especially if you are not interested in paying extra for a higher GPD. For those looking to upgrade to an entire reverse osmosis filtration system for their home, No products found. has the capacity for customization so that it can serve your aquarium as well as provide you with drinking water.

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Hi, my name is Jordan. I've been in the fishkeeping hobby since my childhood. Welcome to my blog where I help fishkeepers enjoy the hobby by offering free guides, advice, & product reviews. Read more...