Best RO DI System for Aquariums – Reviews of the Best Reverse Osmosis for Saltwater and Reef Tanks

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When I first discovered that you could have saltwater aquariums at home, I was amazed. As a child and even college student, it never occurred to me that those colorful coral reefs were possible for homeowners and hobbyists and not just for public aquariums and places like Rainforest Café.

Of course, I didn’t realize the various types of equipment needed, either, and it never occurred to me that straight up tap water contained chemicals and sediment that’s unsafe for human consumption and aquarium life alike.

But when I did, I started researching reverse osmosis for saltwater aquariums and started learning what it takes to create a healthy, safe environment for my sea-faring friends.

If you’re like I was, you’ll want to do more research on this process of purification, but if you already know your stuff, a few reminders might still come in handy.

And if you’re setting up a saltwater fish tank or reef tank for the first time, you might be unfamiliar with these systems altogether like I once was.

For you, we’ll take a brief look at what they are and how they work. We’ll also provide a few tips on how to determine which aquarium RO system could work for your fish tank setup.

Best RO DI Quick-Find Table

Image Product
  • More filtration stages than pretty much anybody else
  • Quality-made, well-trusted products for years
  • High capacity system
  • More filtration stages than pretty much anybody else
  • Quality-made, well-trusted products for years
  • High capacity system
  • Guaranteed 0 ppm water
  • Easy to install air and leakproof system
  • Designed specifically for use with city tap water
  • Guaranteed 0 ppm water
  • Easy to install air and leakproof system
  • Designed specifically for use with city tap water
  • Very portable and easy to use
  • Uses five full stages for nearly complete purification of water
  • Affordable and high-quality
  • Very portable and easy to use
  • Uses five full stages for nearly complete purification of water
  • Affordable and high-quality
  • Comes with a pressure gauge
  • Compatible with external connector hoses for extended reach
  • Super easy to set up and use
  • Comes with a pressure gauge
  • Compatible with external connector hoses for extended reach
  • Super easy to set up and use
  • Powerful four-stage system for purification
  • Comes from a well-trusted brand
  • Compact and easy to use
  • Powerful four-stage system for purification
  • Comes from a well-trusted brand
  • Compact and easy to use

What Does an Aquarium Reverse Osmosis System Do?

Simply put, a reverse osmosis and deionization system – or RODI – is a complicated filter that runs the water supply through three to four stages to produce fresh, clean water.

best reverse osmosis filter fish tanks

The first stage removes particles and crud – the things large enough to see – from the water, eliminating the issues with clogging.

Then, the water is passed through the next stages of carbon filters and reverse osmosis membranes to remove chemicals, chlorine, and other things that make your water unsafe for consumption, whether for your drinking water or for the fish who swim around in the water.

Why is Getting the Best RO System Important?

Have you ever purchased an off-brand filter for your water pitcher? Ever noticed how the water doesn’t taste as fresh, how the filtering process takes longer, and how the filter just doesn’t seem to quite do as well as the brand-name option?

Choosing a low-quality and poorly made RO DI system is kind of like that.

It won’t do as good a job, it won’t work as well, and overall, you’ll technically be okay, but you won’t be satisfied with how you spent your money.

Are RO Systems Mandatory for a Healthy Aquarium?

While many folks may argue that these systems are critical, even mandatory, for a healthy aquarium environment, it’s not technically necessary to have a RODI system for reef tanks in place.

They do provide cleaner, chemical-free water filtered from your tap, however, which is one of the main reasons aquarists insist on their use.

The purified water created by the RO system can then be blended with the appropriate aquarium salts, minerals, and other additives that can then create the perfect environment for your aquarium.

There are, however, other systems that can be used to purify water for use in aquariums, such as carbon filtration, but they won’t result in as pure water as an RO system can create.

Reviews of the Best RO DI System for Reef Tanks and Saltwater Aquariums

I’ve categorized the RODI systems below as best I could to help you sort through for your own tank size, system needs, et cetera. Please review each option’s breakdown if you have any extra questions or concerns regarding the basic specs.

You should find all the info you need to determine which system would be best for your saltwater aquarium or reef tank setup.


#1. Koolermax AR-122

Koolermax AR 122 6 stage RO DI Aquarium Reef RO system 80 to 120 GPD New complete

Koolermax has been around for 18+ years, making RO units for use with drinking water, aquariums, and more. The systems are reliable and come with a solid warranty and money-back guarantee that you can trust backs the high-quality of the product.

The system uses six stages to filter your water, starting with a 5-micron sediment filter that gets rid of rust, dirt, and other sediments.

Next, the second stage filter is a coconut shell activated carbon block filter that removes odor, chlorine, and chloramine.

The third stage repeats the second and then moves into the fourth stage using the reverse osmosis membrane to remove 98% of the contaminants and dissolved minerals still in the water.

The fifth and sixth stages use the DI filter to further purify and reduce minerals in the water for the cleanest filtered water out there.

Here’s the breakdown:

  • Capacity: 80 to 120 GPD – one system
  • Number of stages: 6 filtration stages
  • Ease of use: Very easy to use
  • Comes with: Built-in pressure gauge, installation hardware, automatic shut-off valve

The system is easy to install, but you may need some extra tubing for a far enough reach.

The system doesn’t leak during operation – which is a huge plus – everything is extremely durable and can handle a household of crazy, and the package comes complete with everything you need except the potential extra tubing.

The system comes with a one-year warranty and 24/7 customer support.

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#2. LiquAGen

LiquaGen  5-Stage Reverse Osmosis and Deionization RO DI

Working for up to 75-gallons per day, the LiquaGen 5-stage system is a great option that comes with a great warranty and a guaranteed figure of 0 ppm water.

If you live in the city and use the local water, then this system is for you. The product was designed specifically with city water in mind.

That means the 0 ppm water guarantee holds, the 2-year warranty covers you, and the whole system, using five stages, clears out chemicals like chlorine and chloramine, heavy metals, and other substances found in city water systems.

Here’s the breakdown:

  • Capacity: 75 GPD
  • Number of stages: 5 stages
  • Ease of use: Super easy to use
  • Typical rejection rate for filtration: High rate
  • Comes with: Basic kit, auto-off valve and check if you use a storage tank – free of charge

The LiquaGen 5-stage system takes the water through the typical filtration of pre-filtering via the sediment pre-filtration, multi-stage carbon pre-filtration, the reverse osmosis membrane filter, and finally the de-ionization treatment to give you clean, clear water your fish can breathe in happily.

The systems have been air-leak tested to provide you with the best efficiency possible.

The system has also been designed with leak-free fittings and long-lasting filters to keep the system running long and smooth without wasting water.

TDS should not exceed 350 with this system.

The LiquiGen system comes with a 2-year warranty and lifetime customer support.

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#3. Reverse Osmosis Revolution

Countertop Portable Universal 5 stage Reverse Osmosis RO Purification Water System

If you’re looking for an affordable, high-quality, and extremely portable option, you’ll want to look into the Countertop Portable Universal 5-stage system from Reverse Osmosis Revolution.

This system sits comfortably on your counter while you process the water through five-stages of strong filtration for super clean water for your aquarium.

Attach the system to your kitchen faucet for removal of 93-96% of the arsenic in the water systems, 86-90% aluminum, 95-98% sulfates, mercury, and other contaminants that can make your fish ill.

Affordable and high-quality

The system comes standard with the basics for whatever you need to purify your aquarium water through a high-quality 5-stage process at about 3-gallons per hour.

The system uses the pre-filtration of sediment filters and carbon filters, followed by stages four and five through the reverse osmosis membrane and finally the de-ionization filter that results in a near 0 ppm water quality.

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#4. AquaFX Barracuda

AquaFX Barracuda RO DI Aquarium Filter

The AquaFX Barracuda ROI Aquarium filter is a four-stage RODI system that provides you with a clean, clear 50 to 100 gallons of water for your aquarium.

The system not only includes the standard filtration but also engaged a 2-micron chlorine guzzler carbon block filter and a high-flow, high-rejection TFC membrane – thin-film composite – for deeper filtration and purer water for your fish.

The system is made of solid aluminum “no-rust” metal mounting, clear filter cartridge housings, a pressure gauge, shut-off valve, filter wrench for easy cartridge replacement, feed adapter, and quick connect fittings for the easiest installation and longest lasting functionality possible.

Here’s the breakdown:

  • Capacity: 50 gallons or 100 GPD – your choice
  • Number of stages: 4-stages with 2-micron chlorine guzzler
  • Ease of use: Easy to use
  • Comes with: Standard kit

The filtration system uses 1-micron sediment pre-filtration, followed by 2-micro chlorine guzzler carbon block pre-filtration, and the brand’s exclusive chlorine and chloramine-removal filters.

The system reduces water to zero TDS and maintains PSI between 40 and 60 during operation for efficiency without damaging the product.

The Barracuda is easy to set up and connect with the short hoses and external connectors.

The two sizes available have limited price differences, so we’d recommend getting the larger option in case you ever decide to upgrade to a larger aquarium.

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#5. Aquatic Life RO Buddie

Aquatic Life RO Buddie Four Stage Reverse Osmosis System

This is straight up one of the best RODI systems for aquariums. There’s a good reason for it showing up on our list. It’s a high-quality, budget-friendly option that does a thorough job of purifying your aquarium water through its multi-stage system.

The Aquatic Life system filters out sediment and chemicals easily and reasonably quickly – if used in the right size aquarium – with its three or four-stage filtration system.

First, a sediment filter removes the rubbish floating around in the water, clogging up the system.

Next, the system pushes the water through carbon and then de-ionization filters and RO membrane to produce clean, clear water for use in your aquarium.

Here’s the breakdown:

  • Capacity: 50 or 100 GPD
  • Number of stages: 3 or 4 – your choice
  • Ease of use: Extremely easy
  • Typical rejection rate for filtration: 1:4.5
  • Comes with: Faucet adapter
  • Add ons: Drinking water filtration kit, 4th stage DI kit

The system is very small, making it easy to place under your cabinet or in limited space without issue, while the sediment and carbon pre-filters are easy to access and replace.

The 4-stage systems include a DI color changing mixed bed DI resin cartridge and use a thin-film composite membrane RO cartridge in conjunction with the carbon, mixed bed DI, and sediment cartridges to remove chlorine, heavy metal ions, and the dissolved solids from municipal tap water systems.

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How to Choose the Right Reverse Osmosis System

To help make sure you’re finding the right reverse osmosis for saltwater aquarium system, we’d like to make some suggestions on what to look for and pay attention to as you shop.

We applied these principles in our own reviews below, but we know you’re probably not the only thing you’ll look at.

Hopefully, our tips will get you through the process quickly and less painfully than others, and you’ll walk away with the best RODI system for aquariums and reef tanks possible.

Compare the System to Your Aquarium Size

The first and most obvious thing you can do to determine if the system is right for you is comparing the system’s capacity to your aquarium size.

How much water do you need purified?

How long are you willing to let the system take to run through the purification process each time?

Technically, you can use a small RODI system for a large reef tank, but it will take longer to run the full amount of water through the system. You’ll also have to do a bit more maintenance than you would with a system designed for a larger aquarium.

Look at the Size of the RODI System

Similar to our first point, the size of the RODI system will have a huge impact on the effectiveness of the system for your particular aquarium needs.

Systems come in different sizes designed to work with different aquarium sizes. Be sure to look closely at the capacity of the system before you make your purchase.

Consider the Price of the RODI System

There are, of course, a wide range of systems out there, which means a wide range of prices for those systems. The higher the quality, presumably the higher the price. This may or may not be true, though generally, the better brands will charge more to cover the higher costs of their labor and material costs.

And while the best of the best will be reasonably priced for many, there are still cheap reverse osmosis filter for aquarium choices that work for those with a lower-end budget. These are not automatically disqualified. Just read the reviews from real-life users and professional reviewers to verify budget-friendly doesn’t mean crappy quality.

High-quality products are important, but affordability is, too. Be sure you create a budget that’s reasonable for your wallet and save up for a higher quality option in the future if need be.

Understand the Effectiveness of the System at Purifying Water

Finally, and perhaps the most important part of choosing a reverse osmosis aquarium system is knowing how effective a given system is. There are many quality choices out there but there are also the junk systems that don’t do much, like those off-brand water pitcher filters.

Look for systems and brands that have great reputations – even if budget-friendly – for producing clear, lean, purified water for aquariums.

Do your research. Read the reviews thoroughly and not just the advertiser and retailer ads. Verify the systems come with warranties and money-back guarantees.

saltwater reef aquarium best ro di systems

Finding the Best RODI System Doesn’t Have to Be Hard

The absolute best environment for your saltwater aquarium, reef tank, or freshwater fish tank will come through using a system like the RODI systems we’ve listed above.

The systems clean the water, remove sediment, chemicals, and nitrates, among other things, and give you water that you can then condition to meet the needs of your aquarium pals’ best health.

A good RO water system for aquariums will last for a long time, use non-corrosive materials for their construction, provide three to six filtration stages, and provide enough fresh, clean water for the size aquarium you use.

But to guarantee you’re getting the best RODI filter in your price range, be sure to read the most recent real-life user reviews.

This will help let you know if the retailer is selling the genuine product, if there is a batch of bad products going out, or if there are any other current issues that may be short-term for a given brand.

FAQs for Reverse Osmosis Systems

What is osmosis exactly?

Osmosis is the process of molecules passing through a membrane from a less concentrated solution into a more concentrated solution. This process equalizes concentrations on each side of the membrane.

What is reverse osmosis and how is it different from osmosis?

Reverse osmosis is the process in which a solvent passes through the porous membrane in a system, in the opposite direction of natural osmosis. This happens when the substance is subjected to hydrostatic pressure that’s greater than the osmotic pressure.

How does reverses osmosis help an aquarium system?

Reverse osmosis removes chemicals and sediment from water for purer drinking or aquarium water use.

Where does my RODI system go?

Generally, RODI systems are stored under sinks or cabinets. Some, however, may be stored elsewhere if they are designed for counter-top use.

How hard are RODI systems to install?

Most systems come with clear, easy-to-follow instructions that most people find easy to use for installation. If you tend to be not-so-handy, you may need to find a contractor capable of installing the system for you instead.

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