10 Best Reverse Osmosis Systems for Reef Tanks and Saltwater Aquariums

BEST OVERALL

Koolermax Aquarium Reef Reverse Osmosis Water System

PREMIUM CHOICE

AquaFX Barracuda RO/DI Aquarium Filter

GREAT VALUE

Aquatic Life Reverse Osmosis Water Filtration Unit

A reverse osmosis unit is a worthy and necessary investment for any reef tank or saltwater aquarium owner. Saltwater organisms can be extremely sensitive and they require a safe, hospitable, and healthy environment to be able to thrive. A RO system provides just that, and it’s particularly beneficial for corals because it prevents the overgrowth of algae. However, with so many choices available, it can be tricky to decide which RO system is best for your needs. Our review of the best RO systems will help you narrow down your search.

Table of Contents

BEST OVERALL

Koolermax Aquarium Reef Reverse Osmosis Water System

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This is one of the most powerful RO/DI water systems available as it performs a 6-stage purification, which ensures that the water has all the necessary nutrients and that is safe for your aquatic pets. It includes a high-capacity, 150 GPD membrane and it can generate 120 gallons per day, or approximately 5 gallons per hour. The first 3 stages involve sediment and carbon filtration, the fourth stage is the high capacity membrane that further reduces the level of total dissolved solids (TDS), and the fifth and sixth stages involve color-changing DI filters, which have their resin turn black to indicate exhaustion. Compared to other models, this filtration system has a relatively low water wastage ratio. In addition to aquariums, this system is suitable for misting, aeroponics, hydroponics or anything else that requires extremely pure water applications. It comes with all the tubing and installation equipment, including the additional garden hose adapter.

What We Like Most

6-stage purification

High-capacity RO membrane filter

Color-changing DI filters

All tubing, tools, and extra garden hose adapter included

Free tech support

Our Synopsis:

This is a great option for reef tanks and saltwater aquariums because it performs a 6-stage filtration, which removes pretty much all possible contaminants from the water. It is designed to be connected either to your water supply line under the sink or to a garden hose valve.

Analyst Rating

PREMIUM CHOICE

AquaFX Barracuda RO/DI Aquarium Filter

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This product is ideal for those who need smaller filters and don’t require an extremely fast water outflow, as it provides a 4-stage water filtration and it can generate 100 GPD. With suitable water storage, you can leave it running for several hours during the day or night. The system includes a sediment filter, a chlorine guzzler carbon filter, a high-rejection membrane, and a color-indicating DI resin cartridge. The TFC membrane is extremely efficient and it ensures that TDS in your tank is zero. This filtration system also comes with a pressure gauge that reads 160 psi and a hose adapter. It’s made of aluminum for increased durability and stronger resistance to rust. It’s very easy to assemble and you get all the necessary tools for installation. However, you should expect a relatively high water wastage ratio, so you’ll have to recirculate the excess water to the drain or outside.

What We Like Most

4-stage filtration

Efficient TFC membrane

Pressure gauge included

Color-changing DI filter

Made of durable aluminum

Our Synopsis:

This is a great and budget-friendly option for saltwater and freshwater aquariums. Despite the relatively high water wastage ratio, you get an effective 4-stage filtration and a long-lasting water system.

Analyst Rating

GREAT VALUE

Aquatic Life Reverse Osmosis Water Filtration Unit

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This product is great for those who are on a budget, but still want a highly-efficient reverse osmosis water system. It provides a 4-stage water purification and it generates 75 gallons per day. The RO membrane removes up to 98 percent of total dissolved solids, including lead, arsenic copper, parasitic cysts, and more. The color-changing DI filters remove the remaining TDS from the water, creating a safe and clean environment for your fish and corals. The biggest perk of this system are its twist-in cartridges that can be replaced without the use of tools, you can simply twist them in and out as required. You’ll also get all the gear necessary for setup, including tubing, water supplies connector, and a drain connector.

What We Like Most

4-stage water filtration

Highly-efficient TFC membrane

Color-changing DI filters

Twist-in cartridges

Installation parts included

Our Synopsis:

This product provides a solid outflow and it comes with a highly effective TFC membrane that will get rid of almost all contaminants you can think of. It’s also easy to assemble and it includes a float valve so that it can automatically fill your aquarium.

Analyst Rating

4

Aquatic Life RO

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This is another budget-friendly option that still delivers. This product comes with a 3-stage filtration and it generates 100 gallons of water per day. It includes sediment and carbon cartridges, which are placed up front and easy to replace, a membrane, a membrane wrench, and a faucet adapter. The 3-stage filtration will remove heavy metal ions, total dissolved solids, and other hazardous substances from the water. The system’s compact size makes it easy to install it even if you have a limited amount of space at hand. Also, you’ll get mounting brackets, which secure the unit in place during the mounting process. This RO system is easy to maintain and it allows you to upgrade to a fourth stage of water filtration by adding a DI filter.

What We Like Most

3-stage filtration

Up front and easy-to-replace cartridges

Includes a membrane, a membrane wrench, and a faucet adapter

Compact size

Additional filtration stages can be added

Our Synopsis:

This is a highly affordable option for aquarium owners that provides a 3-stage filtration. It’s easy to install and it doesn’t take a lot of space, so you’ll be able to find a convenient location for it.

Analyst Rating

5

Express Water Reverse Osmosis Deionization Water Filtration System

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Another super powerful RO-DI water unit like this product will work well for reef tank and saltwater aquarium owners. This model provides 6-stage filtration that removes up to 99 percent of contaminants, including nitrates, arsenic, calcium, lead, and much more. The DI water filter is made with ion exchange resin beads, which enables it to purify the water to a great extent, and it makes this system suitable for a variety of uses, including aquariums, cooking, cleaning, and watering plants. This RO-DI system has a superb filtration system that’s easy to set up, automatically fills your tank, and it comes with an emergency stop leak detector that turns off the water flow if there is leakage. Also, you can upgrade the unit with additional filtration stages, such as an alkaline water filter or a UV water filter.

What We Like Most

6-stage filtration

Removes up to 99 percent of all contaminants

Upgradable and customizable filters

Easy setup

1-year warranty

Our Synopsis:

This product provides a powerful performance in the form of a 6-stage filtration, which will ensure that your aquarium water is free of contaminants and safe for your fish and plants. Another great perk is that you can add more filtrations according to your needs.

Analyst Rating

6

Reverse Osmosis Revolution Portable Water Filtration System

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This model provides 5-stage filtration to make your water ultra pure and it includes a high-rejection membrane that removes up to 99 percent of all kinds of contaminants. It’s extremely easy to install and it generates 3 gallons of water per hour. All the filters come with quick connectors and the DI filter is made with ion exchange resin beads to make sure the water is extra pure. It’s designed to be able to attach easily to a kitchen faucet or a garden hose, and it’s compact size makes it a great portable solution for aquariums, apartments or RVs. It’s important to mention that if you want to connect your system to a garden or laundry hose, you’ll need to specify that in the Customer Notes, and they will replace the 2-way diverter for kitchen faucets with a hose adapter.

What We Like Most

5-stage filtration

High-rejection membrane

Removes up to 99 percent of contaminants

Easily attaches to a kitchen faucet or a garden hose

Compact size

Our Synopsis:

This is a great, long-lasting solution for aquariums because it offers a high-quality filtration system with an extremely effective TFC membrane. It can be attached to kitchen faucets or garden hoses and you can set it up in no time.

Analyst Rating

7

iSpring RCC7D 5GPD Under Sink 6-Stage Reverse Osmosis Drinking Filtration System

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This is another great-functioning RO unit that offers a 6-stage filtration to ensure you get a crystal clear and pure water for your aquarium. It has a highly effective TFC membrane that reduces the amount of total dissolved solids to zero and eliminates all sorts of contaminants. The membrane will have to be replaced approximately every 2 years. This system is pretty easy to set up and because of its compact size, you won’t have trouble finding it a suitable location. It includes a solid brass body faucet with a nickel finish. The unit produces a relatively slow outflow and for every 1 gallon of water, there are 2 or 3 gallons of water wastage, so it will need recirculating the wasted water outside or to your drain.

What We Like Most

6-stage filtration

High-rejection TFC membrane

Completely removes total dissolved solids

Compact size

1-year warranty

Our Synopsis:

This is a great option for all aquarium owners who want extremely pure water, but don’t require incredibly fast outflow. The setup is very easy, and you get written, video, and tech support.

Analyst Rating

8

APEC Reverse Osmosis Water System

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This RO-HI system provides 5-stage filtration that removes up to 99 percent of contaminants and it filters over 1000 water pollutants. It has a quick-dispense design that provides a relatively fast water output, so you won’t have to wait long to fill your tank. The high-rejection membrane combined with a coconut shell-refined carbon as the last filtration stage makes sure to eliminate any possible residue from the tank. The unit is easy to install and maintain, as the filter can last up to 12 months. It has a solid construction that prevents leaks and it operates silently.

What We Like Most

5-stage filtration

High-rejection TFC membrane

Total Contamination Removal filter in the last stage of purification

Easy assembly

2-year warranty

Our Synopsis:

This is a great option for aquarium enthusiasts because it offers a highly effective, 5-stage filtration process that helps you eliminate harmful chemicals almost entirely. It’s a durable product that provides a relatively fast outflow.

Analyst Rating

9

SpectraPure MaxCap RO/DI System 180 GPD

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This model generates an impressive 180 gallons of water per day and it provides 4-stage filtration with a DI filter that ensures extra pure water. It has a manual flush valve that preserves membrane and makes it last longer. The membrane is highly effective, particularly when it comes to removing phosphate and silicate. This RO-DI unit comes with improved filters that have 4 times greater capacity than regular ones. Another perk are two dual-probe inline meters that measure the performance of the membrane and DI cartridge respectfully. This system has a low water wastage ratio (2:1), so you’ll get a significantly lesser amount of excess water compared to other models. It includes a pressure gauge that indicates when to change pre-filters. It also comes with a housing wrench for easy filter removal, a mounting bracket, and a hose adapter.

What We Like Most

4-stage filtration

DI filter

Low water waste ratio

Two dual meters that measure the performance of the membrane and DI filter

3-year warranty

Our Synopsis:

This is a great choice for reef tanks or aquariums because it offers quality RO-DI filtration and it provides an extremely fast water output. It also comes with high-quality membrane and filters.

Analyst Rating

10

LiquaGen 5-Stage Reverse Osmosis/Deionization Unit

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This is another extremely efficient RO-DI system that provides 5-stage filtration and it has a high-rejection membrane and DI filter that remove contaminants and reduce the number of total dissolved solids to zero. Filters are designed with durability in mind and they have leak-free fittings, which minimizes the chances of breakage or damage. The system’s operating water pressure ranges from 50 psi to 100 psi, while operating temperature falls between 39 and 113 degree Fahrenheit. The unit is very easy to assemble and maintain, and first time RO-DI buyers won’t have trouble assembling it. It comes with pre-installed automatic shut-off valve and a check valve, which will be necessary if you plan to use this unit with a storage tank.

What We Like Most

5-stage filtration

DI filter

High-rejection membrane

Pre-installed auto shut-off and check valve

2-year warranty

Our Synopsis:

This is a long-lasting and effective RO-DI unit that provides 5-stage filtration, which will help create a safe and healthy environment for your aquatic pets and plants. There are minimal chances of leakage or breakage thanks to the high-quality and durable materials, and it’s easy to set up and maintain.

Analyst Rating

Buyer's Guide

With advancements in technology, modern reverse osmosis units for aquariums offer plenty of perks and a way to obtain extremely clean water that’s free of almost any contaminants you can imagine. With such a wide selection of products, it can be difficult to decide which one is right for you, especially if you are a novice when it comes to reef tanks or saltwater aquariums. However, there are some factors you need to take into account when purchasing these systems, such as the number of stages it provides, the quality of the membrane, capacity, and ease of use.

The Number of Stages

Reverse osmosis systems typically come with 3, 4 or 6 stages of water filtration, while some even offer additional filtration options for extremely pure water, such as UV filters or alkaline filters. The minimal amount of stages you need is 3, anything less is considered to be of poorer quality and it could compromise the wellbeing of your fish because the membrane isn’t protected enough. The 4-stage option is the one that most aquarium enthusiasts go for, as it provides effective water purification consisting of the following: a sediment and carbon pre-filters, the membrane, and the DI filter. The higher stages involve adding another DI filter or a carbon filter to further purify the water and protect the membrane A sediment pre-filter protects the membrane and it filters larger particles of sand and other sediments, while a carbon filter is responsible for removing chlorine, which is a common ingredient found in tap water. The membrane is essential part of a reverse osmosis unit and id does most of the job when it comes to removing total dissolved solids (TDS), which include organic compounds, heavy metals, and salts that the water contains. The fourth stage is the deionization process, which involves restoring the water’s balance by adding minerals and getting rid of any remaining contaminants that weren't removed during the previous stages. The DI filter’s resin contains hydrogen molecules that get traded with chemical molecules, hence making the water purer. Once a resin releases all of its hydrogen molecules, it’s time to get a new one.

The Quality of the Membrane

The membrane is the focal point of a reverse osmosis unit because it handles over 95 percent of chemical removal. However, it’s extremely sensitive and permeable, which is why it should be protected by the filters that come before it, as their job is to remove bigger particles. It’s extremely important that a membrane is made of a high-quality and durable material, so that it can perform an effective filtration and last for a longer period of time. The most effective type of membrane is the one that’s made of thin film composite (TFC) as it removes 94-98 percent of total dissolved solids. TFC membrane is more often found in units with 6-stage filtration because it can get damaged easily by chlorine, hence the need for a carbon filter that removes this substance from water. Another option is a cellulose tri-acetate (CTA) membrane, but this type has a lower TDS removal score compared to TFC membrane that ranges from 88 to 94 percent. Also, this membrane only functions with chlorinated water, since the lack of chlorine would cause the growth of bacteria on it, so they are never used in 6-stage filtration units.

Capacity

The capacity of a reverse osmosis unit is measured by the maximum amount of gallons it produces per day. Typically, RO units with a faster water output will have the capacity of 100 GPD and above. Generally, systems with faster outflow rate are a better option because they take less time to fill the tank, which will also save you some time, as you won’t have to sit around and wait long for the tank to become full.

Easy Setup and Maintenance

It goes without saying that you should choose a product that is easy to install even if you’ve never used it before. Majority of reverse osmosis units are pretty easy to set up and they come with all the equipment you need. They also include instruction manuals and sometimes even video support. Another important feature is how easy it is to maintain a reverse osmosis unit. You’ll want a product that allows for easy installation of new parts in case of breakage. For example, some RO units come with twist-in cartridges that can easily be replaced, without the use of tools.

How long does a reverse osmosis unit last?

A RO system can last for an indefinite period of time as long as you regularly replace the old parts with new ones when they wear out. On average, membrane can last from 2 to 5 years, depending on the nature of water it filters. Carbon filters should be replaced every 6 to 12 months for optimal performance.

Does a reverse osmosis unit need electricity?

RO units don’t require electricity to keep them running as they operate with the help of water pressure. However, if you add UV lamps or pressure booster pumps to your system, these items will require electricity to power them.

Why do you need to measure the amount of total dissolved solids in water?

Total dissolved solids are commonly contained in water and they encompass substances such as salts, heavy metals, and organic compounds. Having low amounts of TDS in your tank won’t necessarily cause you problems, but higher amounts of it can lead to algae buildup, which can be harmful for fish and corals. It’s a good idea to aim for having zero TDS in your aquarium, which can easily be achieved if you invest in a quality reverse osmosis unit with a high-rejection membrane that will be able to remove the solids completely. Fortunately, it’s easy to measure the amount of TDS your tank contains so that you can reduce the number if necessary. Many RO units come with built-in TDS meters, but if the one you purchased doesn’t, you can buy it separately. These devices are affordable and reliable, and they are necessary for maintaining optimal water quality for your reef tank or saltwater aquarium.

How much gallons of water per day do you need?

As we’ve mentioned above, the number of gallons produced per day refers to the flow rate of water that gets released, and how much you need will depend on the size of your tank, whether you use a storage tank as well, and how often you flush the water. If you want to determine the minimal amount of GPD you need, you have to divide the size of your tank in gallons by the number of days between water changes. However, if your RO system is connected to a water storage tank, you’ll be able to produce a higher number of gallons than the minimum you need, so you can change the tank water by pulling from your storage container. The RO systems that provide faster water output will save you some time waiting for your tank to fill, so they are generally a better choice, although you can opt for slower alternatives if you have free time at hand, speed will not affect the quality.

What is the difference between a RO water and a RO-DI water?

RO water and RO-DI water are similar in many respects, but they also have a few key differences. RO-DI stands for reverse osmosis deionization, so water that goes through this type of filtration goes through the process of deionization in addition to reverse osmosis. This means that the water goes through additional filtration stages that enable it to become extremely pure as they eliminate any remaining water pollutants. Also, through the process of deionization, the water receives back some of the nutritious minerals that are necessary for maintaining a hospitable and safe environment for the fish and plants.

Why is water pressure important for proper functioning of a RO unit?

Water pressure is essential because it’s responsible for the flow of water through the membrane and for the flushing of contaminants away. Low pressure can hinder water production and it can damage the membrane. The optimal amount of pressure for a RO unit is 60 psi. If you have a pressure below 40 psi, it probably won’t be enough to keep the system working, and you’ll need to increase the pressure with a pressure booster pump.

Expert tip

Adding a water softener can make the membrane last longer. The sodium that gets added to the water through the softener is much gentler on the membrane as it is able to remove up to 98 percent of this substance.

Did you know

When saltwater evaporates from a tank, it leaves the salt behind, so you should refill it with freshwater to keep the salinity level unchanged.

Conclusion

After reviewing the options above, you should be able to have a clear picture on what type of reverse osmosis unit you need. Take into account the size of your tank and think about how many filtration stages you actually need. Also, look for products that are sturdy and have a quality membrane that will be able to filter your water efficiently for years to come.