9 High-Performance RO DI Systems for Your Reef Tank

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Uncontaminated saline water in your tank is really essential in sustaining all creatures’ lives inside. 

And getting a RO DI system (reverse osmosis system) is the simplest way to make sure the tank water is properly suited. 

Water, in its natural condition, can never be pure because of pollutants and other dissolved compounds. If your water system has no fine filtration, the pollution can continue to happen and do harm to sensitive marine inhabitants.

This article will walk you through a hand-picked collection of the best RO DI systems that can par excellence maintain your reef aquariums.

About RO/DI Systems

If you’re a novice in the aquarium field, let us explore some basic information about the RO DI system.

What is the meaning of RO?

Basically, RO or reverse osmosis is a powerful purification mechanism with its multi-stage filtration process. 

As a crucial natural phenomenon, osmosis happens when water with a lower saline level moves to water with higher saline levels.

Accordingly, reverse osmosis is the reversal of that phenomenon. Rather than low going to high, the higher saline water is drawn via a semipermeable membrane like a filter. While water transfers through the filter, most other compounds (bacteria, organics, or salts) are kept, which results in pure water. 

The initial stage of the RO filtration is when pressurized water passes through a pre-filter, which eliminates micron sediment (silt, sand, or clay sediment) that would constrain RO membrane functionality. 

In the next stage, the semi-filtered water migrates through an activated carbon filter, which captures a variety of pollutants and minerals, such as chromium, chlorine, pesticides, etc. 

Now the water has gone through the RO filtration system; then it passes into the deionization stage.

As water migrates through the deionization (DI) cartridge, both positively (cations) and negatively (anions) charged ions would be removed and replaced by hydrogen (H+ and H-) ions, thanks to synthetic resins. 

This truly sounds extremely complex, right? However, you just need to grasp that this purification process can remove detrimental chemicals and compounds, as well as modify the molecular structure of water. 

Why does an RO/DI System Matter?

You have to get a RO DI System for your aquarium because tap water is full of impurities that might lead to nuisance algae growth. 

Total dissolved solids (TDS) are a measurement that includes organic matter and salts dissolved in the water. A high volume of TDS in your water means that you provide nutrients that algae love. And you will never fight against nuisance algae. 

A standard 4-stage RO DI system involves the 4 fundamental steps to filter your input water down to 0 TDS. That means the tap water will be pure H2O with no other contaminants and dissolved compounds. For cases in which the RO DI system is heavily used, or the source water is seriously polluted, it may be beneficial to invest in a 5 or 6-stage system in which an additional carbon or deionization stage is added. 

Tips for Choosing an RO/DI System 

One of the most substantial things to know about RO DI systems is that they create small quantities of water per hour. The filtration process will generate from 50 to 100 gallons on a daily basis, according to the system you choose.

You can enhance RO performance by including an optional water pressure booster pump. This pump is a small low-voltage pump that keeps the maximum pressure for the RO DI filtration process. In case the water pressure is less than 50 psi, you can use an RO booster pump to achieve the desired performance out of your filter system.

Some RO DI systems are equipped with a water stage tank that contains clean water. You can pick an RO DI system with a lower output if you already own a storage tank.

Some aquarists simply store the purified water in plastic buckets. This can be dangerous if you don’t check on the bucket regularly and it might overflow. The storage tank will reduce the possibilities of overflow and you don’t need to wait around for the water to be produced.

You also should remember to replace the individual filter cartridges periodically to preserve water purity. Using a TDS meter will allow you to determine the overall level of dissolved minerals in the RO water.

Your RO DI system should be creating water with a TDS range of 0-20 parts per million as measured with a TDS meter. If the TDS level begins to increase above 50 ppm, the RO membrane and DI resin need to be changed. 

Top 9 High-Performance RO/DI Systems

1. Aquatic Life Twist-In RO/DI Unit 

Aquatic Life Twist-In 100 Gpd 3-Stage Ro Unit (Sediment, Carbon Block, Membrane)
Aquatic Life Twist-In 100 Gpd 3-Stage Ro Unit (Sediment, Carbon Block, Membrane)


  • A comprehensive RO DI system in a compact configuration
  • Reasonable price
  • Easy to change filters


  • Proprietary cartridges

This is an excellent RO DI system with a host of innovative features. It has the ability to produce 100 gallons of purified water per day if it runs at maximum capacity. 

The system involves 4 different stages to eradicates all traces of dissolved solids from municipal or well water. One unique feature of this filter is a twist-in filter system, which helps you change the filters without a canister wrench. 

The initial stage of the system consists of a 5-micron sediment filter. The filter can get rid of large particles from the water before they get to the RO membrane. 

The second stage is the carbon filter which is created by activated carbon. Activated carbon can decrease chlorine by up to 99% and eliminate volatile organic compounds. 

The next stage is the twist-in reverse osmosis membrane that can clear out dissolved solids in the water. This filter might have a lifespan of 1 to 2 years, depending on your water’s quality. 

The fourth stage of this RO DI system involves the deionization filter. It utilizes a blended bed color-changing deionization resin that will turn green into amber if the filter media is fully saturated.

2. Aquatic Life RO Buddie System 

AQUATICLIFE Aquatic Life RO Buddie Plus DI Four Stage Reverse Osmosis Deionization Unit 50 GPD
AQUATICLIFE Aquatic Life RO Buddie Plus DI Four-Stage Reverse Osmosis Deionization Unit 50 GPD


  • Affordable price
  • Simple to use and set up
  • Quick disconnect fittings make it easy to change the filtration components. 
  • A compact item for nano reef aquariums


  • The mounting bracket is snap-fit to the filter components, sagging under the weight of the water. 
  • Users need to use push-pull connectors to prevent any possible leaks. 

If you’re on a tight budget and need a fine RO DI system, you can consider this Aquatic Life unit. The system can create up to 50 gallons of pure water per day.

This RO DI system utilizes the same four-stage filtration process as a full-size one. The difference is that this system employs smaller filter cartridges than the larger one. The benefit of this is that it can fit into narrow spaces, while you have to change the filters more regularly. 

The first two stages of the filter are the sediment filter and the carbon one. The former is a compact RO Buddie filter cartridge that filters the water before it goes into the rest of the filter. In the meantime, the compact carbon cartridge clears out chlorine and other contaminants. 

The third stage is the reverse osmosis cartridge. It is a full-size cartridge, lasting as long as an RO membrane on a bigger unit. 

The final two stages of the filter include the deionization filter. The cartridge is attached with an iron capturing resin that slowly changes color to show when the media stops working. 

Notably, this RO DI system is provided with a sink/ hose bib attachment. In other words, you can utilize the filter without hooking it to your plumbing. 

3. SpectraPure MaxCap RO DI System 

SpectraPure MaxCap RO/DI System
SpectraPure MaxCap RO/DI System


  • An incredible TFC membrane
  • 2:1 waste ratio
  • Dual TDS meters
  • Amazing silicate removing capacity 
  • A 3-year warranty


  • High price 

This amazing SpectraPure MaxCap filter system can produce 90 gallons of water every day with the use of a 99% rejection thin-film reverse osmosis membrane. Markedly, the system decreases its wastewater so that it can create only twice as much waste as clean water, compared to the four times as much released by others. 

The pre-filtration stages of the RO DI system are made up of a 0.5-micron MiroTec Sediment filter and a carbon block filter. The Sediment filter aims to removing any particles from the water, prolonging the life of the RO membrane. Meanwhile, the carbon block does a great job of eliminating any chlorine and other volatile compounds. 

The SpectraPure MaxCap system involves two deionization stages to create ultra-clean ion-free water. Besides, the dual deionization filters extend the lifespan of your DI filter material, so you won’t need to change them often. 

Moreover, the filter contains a pressure gauge on the membrane inlet. It is also packed with a manual membrane flush valve that supports the RO membrane. Plus, all the filter cartridges are translucent, so it is easy for you to notice which filter media needs to be replaced. 

Furthermore, there are two TDS meters included in the system. One gauges the dissolved solids at the inlet, while the other determines the dissolved solids of the completed product. These meters also enable you to monitor the overall performance of the system. 

4. LiquaGen Portable Aquarium-Countertop RO/DI System

LiquaGen - 4 Stage Reverse Osmosis and Deionization (RO/DI) Portable Space Saver Water Purification System - 50 GPD
LiquaGen – 4 Stage Reverse Osmosis and Deionization (RO/DI) Portable Space Saver Water Purification System – 50 GPD


  • Portable 
  • Affordable price
  • Provide a full-size RO membrane


  • Regular filter changes required

For those who are new to RO DI system, this is a perfect option. The LiquaGen RO DI system includes a standard four-stage process.

The first stage of the process is comprised of an inline sediment filter. This will dispose of any rust, dirt, or sand before it goes into the other filter cartridges. In the second stage, chlorine and other volatiles will be removed, thanks to activated carbon.

The next stage involves a full-size RO membrane that can eradicate any lead, radium, arsenic, and other toxic heavy metals from the water. 

The last two stages are made up of the deionization filter. It leverages a resin to wipe out any cation and anion from the water that migrates via the RO membrane. The filter will slowly change from green into amber if a resin change is notified. 

5. LiquaGen Portable – 6 Stage Dual Use RO/DI

LiquaGen Portable - 6 Stage Dual Use (Drinking & 0 PPM Aquarium Reef/Deionization)
LiquaGen Portable – 6 Stage Dual Use (Drinking & 0 PPM Aquarium Reef/Deionization)


  • Tailored to make ultra-pure reef water
  • Provide pressure and TDS monitors
  • Achieve up to 150 GPD at proper conditions
  • Include a garden hose adapter for simple hook-up
  • Include a patented pressure booster


  • Does not come with a storage tank 

This is another RO DI system from LiquaGen, but this one amazingly involves a six-stage filter process. 

The two carbon pre-filters are constructed from various materials – one of UDF – activated carbon and one of coconut carbon – to dispose of a large array of impurities and chlorine. 

In addition, the system comes equipped with a dual inline total dissolved solids meter and a pressure gauge. That allows you to track the output water and identify when to replace the filters. 

This RO DI system can filter water at up to 100 GPD. The TFC reverse osmosis membrane is greatly efficient, removing more than 98% of total dissolved solids. 

What’s more, the filter line contains a manual flush line, supporting to flush the system and prolong the lifespan of the system. Plus, the unit is almost pre-assembled with the flow restrictor already inline; thereby, you can begin experiencing the system as soon as it arrives. 

6. AquaFX Barracuda RO/DI Aquarium Filter

AquaFX Barracuda RO/DI Aquarium Filter, 100 GPD
AquaFX Barracuda RO/DI Aquarium Filter, 100 GPD


  • Include a 1-micron pre-filter that eliminates membrane-clogging iron particles and sand grains
  • The carbon block cartridge is rated for more than 3700 gallons 
  • Use a high-grade USA-made thin-film composite


  • You might need to buy a longer hose to reach the water supply and drain.
  • The manual in the box does not tell much about the operation of the system. 

At full capacity, the AquaFX Barracuda RO DI system can create up to 100 gallons of purified water per day. Its rust-resistant metal frame offers a sturdy and durable mounting system for attachment to a wall.

The compact system consists of a 4-stage filtration process to generate ultra-clear 0 TDS water. The initial stage of the system includes a 1-micron sediment filter that will clear large debris to lengthen the life of the RO membrane. The second stage has an AquaFX carbon block that can get rid of chlorine and other volatile compounds. 

The reverse osmosis membrane works extremely efficiently in the third stage and produces water that measures zero total dissolved solids. 

The fourth and fifth stages involve the deionization filter that can remove any of the rest dissolved solids. This filer leverages AquaFX mixed bed color changing DI resin, indicating when the DI filter media needs to be replaced. 

The manufacture does provide a pressure measurement tool, so you can ensure your water pressure is strong enough to purify the water. Besides, the system is packed with a 0.25-inch hose bib adapter, 6-feet tube, and canister wrench. 

The waste to filtered water ratio on this product is comparatively high – above 4:1. Thus, there might be a lot of wastewater that needs to be recirculated to your drain. 

7. iSpring RCC7D 75 GPD Reverse Osmosis Water Filter 

iSpring RCC7D Water Filter for Sink, 6-Stage Reverse Osmosis Water Filtration System
iSpring RCC7D Water Filter for Sink, 6-Stage Reverse Osmosis Water Filtration System


  • Simple to install 
  • Provide lifetime customer support
  • Include a pressurized storage tank and a nickel faucet


  • The filtering process might be slow at 75 GPD. 

This six-stage RO DI system is specifically designed to fit under the sink while still offering up to 75 GPD when working at optimal pressure. 

The early filtration stages include activated carbon and coconut carbon filters, disposing of chlorine from the reverse osmosis membrane and completely absorbing volatile organic carbons. 

The TFC reverse osmosis membranes excellently eliminate total dissolved solids, and you can keep track of the membrane and deionization filters, owing to the inline dual total dissolved solids matters. 

Moreover, the TFC membrane has a lifespan of about two years, though flushing the system without a manual valve might be more challenging. 

Remarkably, iSpring offers a one-year guarantee and one-year money-back policy on the system, as well as lifetime technical support. 

8. Apec Water Systems Ultimate RO-Hi

APEC Water Systems Ultimate RO-Hi Top Tier Supreme Certified High Output Fast Flow Ultra Safe Reverse Osmosis Drinking Water Filter System, 90 GPD
APEC Water Systems Ultimate RO-Hi Top Tier Supreme Certified High Output Fast Flow Ultra Safe Reverse Osmosis Drinking Water Filter System, 90 GPD


  • The bigger tubing lets you fill a bucket with water more rapidly.
  • Easy to make water changes and top-offs
  • Include dual activated carbon cartridges
  • Include replacement filters
  • Lifetime product support


  • Does not contain a deionization cartridge
  • No pressure measurement tool to track maintenance needs 
  • No flush valve to purge the system

This filtration unit uses 3/8 inches connections and tubing to transfer more water via the system.

The RO can make up to 90 gallons of purified water each day. The Ultimate RO-Hi system involves 5 different stages of filtration.

The polypropylene sediment filter wipes out rust particles that might clog the filter and harm the RO membrane. Two compressed activated carbon filters do a good job of removing chloramine, chlorine, and organic chemicals. 

The US-made RO membrane swimmingly clears out heavy metals, phosphates, nitrates, and other contaminators that can negatively impact your reef tank. 

The final filtration stage helps absorb any trace of organic compounds with a coconut shell-activated carbon cartridge. 

The manufacture also offers a lead-free faucet and a water storage tank to spread the reef-safe water. 

9. Koolermax AR-122 RO/DI Aquarium System 

Koolermax AR-122 6-stage RO+DI Aquarium Reef Reverse Osmosis Water System 150 GPD New Complete
Koolermax AR-122 6-stage RO+DI Aquarium Reef Reverse Osmosis Water System 150 GPD New Complete


  • Durable and sturdy design
  • No leaking problems
  • Provide one-year warranty
  • 2 DI stages for comprehensively water purification and polishing


  • Users can only use filters from Koolermax as they differ from traditional ones. 
  • The guide manual is a bit hard to understand for novices.
  • The system runs best with water sources with less than 300 TDS.

The Koolermax 6-stage reverse osmosis system is a go-to choice for aquarists on a low budget. 

This RO DI system is filled with everything necessary to begin filtering water, like a pressure gauge, so you can track when the carbon pre-filters need to be changed. A wonderful after-market addition is a dual TDS meter to place inline before and after the deionization filters so that you can keep tabs on when to replace the filters. 

If working at maximum pressure, the system can achieve a massive 120 GPD, so you can probably fill a bucket to top off your aquarium in a couple of hours. 

The reverse osmosis membrane can get rid of more than 98% of total dissolved solids, even though compared to the TFC membrane on the SpectraPure system, it only eliminates approximately 90% of silicates. 

Quick Comparison of the best RO DI Systems

#Product NameImagePriceAction
1Aquatic Life Twist-In RO/DI Unit Aquatic Life Twist-In 100 Gpd 3-Stage Ro Unit (Sediment, Carbon Block, Membrane)$$Buy on Amazon!
2 Aquatic Life RO Buddie SystemAQUATICLIFE Aquatic Life RO Buddie Plus DI Four Stage Reverse Osmosis Deionization Unit 50 GPD$Buy on Amazon!
3SpectraPure MaxCap RO/DI System SpectraPure MaxCap RO/DI System$$Buy on Amazon!
4LiquaGen Portable Aquarium-Countertop RO/DI SystemLiquaGen - 4 Stage Reverse Osmosis and Deionization (RO/DI) Portable Space Saver Water Purification System - 50 GPD$Buy on Amazon!
5LiquaGen Aquarium Reef RO/DILiquaGen Portable - 6 Stage Dual Use (Drinking & 0 PPM Aquarium Reef/Deionization)$$Buy on Amazon!
6AquaFX Barracuda RO/DI Aquarium FilterAquaFX Barracuda RO/DI Aquarium Filter, 100 GPD$$Buy on Amazon!
7iSpring RCC7D 75 GPD Reverse Osmosis Water Filter iSpring RCC7D Water Filter for Sink, 6-Stage Reverse Osmosis Water Filtration System$$Buy on Amazon!
8Apec Water Systems Ultimate RO-HiAPEC Water Systems Ultimate RO-Hi Top Tier Supreme Certified High Output Fast Flow Ultra Safe Reverse Osmosis Drinking Water Filter System, 90 GPD$$$Buy on Amazon!
9Koolermax AR-122 RO/DI Aquarium System Koolermax AR-122 6-stage RO+DI Aquarium Reef Reverse Osmosis Water System 150 GPD New Complete$$Buy on Amazon!

A RO DI system is an integral, effective, economical method to create highly pure water in large quantities for your reef tank. 

These superior systems range in the number of filtration stages they provide and the membranes they utilize, but the best ones strikingly eliminate dissolved solids, minerals and deionize the water to build a healthy environment for your inhabitants. 

If you’re looking for a perfectly featured six-stage filtration system, then you can choose either LiquaGen Aquarium Reef or SpectraPure units. Meanwhile, the AquaFX RO DI system turns out to be the most proper choice if you want to save money or don’t require such a high water purity level in your fish tank. 

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