Reverse Osmosis Deionization: 5 Top Rated Filtration Units

Using high-quality water is the key to having a beautiful, healthy aquarium.

Your fish, corals and other invertebrates, as well as live aquatic plants, thrive only if the aquarium water is suitable for their particular requirements.

Tap water is rarely ideal for freshwater and marine aquariums. Your water may have too many minerals for most tropical fish. It could also contain algae-promoting nutrients.

My picks are the RO Buddie and the iSpring , keep on reading for more options!

Water treatment plants add chemicals that make the water safe to drink but unsuitable for aquarium use. Experience shows that fish, plants, and corals live longer and look better when purified water is used in the aquarium.

Fortunately obtaining purified water for your aquarium is easy. A reverse osmosis deionization (RO/DI) filtration system will provide you with clean, clear water that is free of contamination.

This guide will help you select a good RO/DI unit that meets the needs of your type of aquarium.

What is in my tap water?

Why unfiltered tap water causes trouble in the aquarium

The goal of every aquarist is to maintain the best possible water quality and do it consistently. A stable aquatic environment is essential for a thriving aquarium. If your tap water contains an extreme level of minerals, pH, and nutrients, it will be difficult or impossible to maintain stable water conditions.

Let’s take a look at a few common examples where unfiltered tap water makes aquarium keeping a struggle.

Amazonian aquariums

Saltwater fish aquariums

Reef aquariums

How does a reverse osmosis filter with deionization work?

Tips for selecting an RO/DI filtration system for your aquarium

  • One of the most important things to understand about reverse osmosis filters is that they produce small amounts of water every hour. The filtration process will produce 50 to 100 gallons per day depending on the system you select.
  • You can improve RO performance by adding an optional water pressure booster pump. An RO booster pump is a small low-voltage pump that maintains the optimal pressure for the reverse osmosis filtration process. If your water pressure is less than 50 psi, consider installing an RO booster pump to ensure you get the best performance out of your filter system.
  • Some RO/DI systems come with a water storage tank that collects the purified water. You can select an RO/DI filter system with a lower output if you have a storage tank since it will automatically store excess water. Many aquarists simply collect the filtered water in plastic buckets. This can be risky if you forget to check on the bucket and it overflows. The storage tank eliminates the chances of overflow and you don’t have to wait around for the water to be made.
  • The individual filter cartridges will need to be replaced periodically to maintain water purity. One of the best ways to check the performance of your RO/DI filter system is with a hand-held Total Dissolved Solids (TDS) meter. The TDS meter measures the overall level of dissolved minerals in the RO water. Your RO/DI system should be producing water with a TDS range of 0-20 parts per million as tested with a TDS meter. When the TDS level starts to creep up above 50 ppm, it is time to change the RO membrane and DI resin.

Top five RO/DI filtration systems for aquariums

1. AquaFX Barracuda RO/DI Aquarium Filter 50GPD

The Barracuda RO/DI system uses four stages of filtration in a compact configuration that stores easily under a sink cabinet.

The rust-resistant metal frame provides a sturdy mounting system for attachment to a wall.

The blue-tinted filter housings might make it difficult to see the deionizing resin change color.

The AquaFX Barracuda RO/DI filtration system is available with a 50 gallon per day flow rate or a high-capacity 100 gallon per day model.

Consider a Watts Premier Water Filtration Booster Pump Kit if your water pressure is below 50 psi.


  • Comes with a 1-micron prefilter that removes membrane-clogging iron particles and sand grains. This protects the rest of the filtration system.
  • Chlorine-removing activated carbon block cartridge is rated for over 3700 gallons before replacement is required.
  • Uses a high-quality USA-made thin film composite (TFC) reverse osmosis membrane for long life and consistent performance.
  • The mixed bed deionization cartridge comes with color-changing resins that indicate when the resin needs to be replaced.
  • The filter system includes a water pressure gauge that indicates when the RO/DI system needs service.


  • The hose kit is adequate but if you need a longer hose to reach the water supply and drain, you’ll have to buy longer hose or splice the sections together.
  • Works best when your water pressure is above 50 psi. If you have a well you may need a booster pump to attain 50 or 100 gallons per day output.
  • The manual in the box mentions more about the rest of the product line and not much about the operation of the filtration system

2. Aquatic Life RO Buddie 4-Stage Reverse Osmosis System

The RO Buddie is an economical four stage starter RO/DI filtration system for freshwater or marine aquariums.

It is a compact design that can be mounted in tight locations. It is ideal as a temporary RO/DI filtration system that can be quickly set-up and stored away when not in use.

Many aquarists with smaller aquariums use a portable system like the RO Buddie.

The filter can be placed in the sink or in the shower when filling up a bucket of water.

The RO Buddie provides sediment filtration, chlorine/chloramine removal, eliminates minerals, nutrients, and heavy metals.


  • A complete RO/DI system in a compact configuration.
  • Quick and easy set-up.
  • Color changing deionization resin cartridge is made of clear plastic for easy viewing.
  • Quick disconnect fittings make changing the filtration components easy.
  • Makes 50 gallons per day


  • Does not come with hose to connect the faucet to the filtration system and wastewater drain line.
  • Mounting bracket is snap-fit to the filter components and can sag slightly under the weight of water.
  • Tight radius of the tubing may pose a potential leak hazard if not carefully handled.
  • Instruction manual contains minimal tips and instructions.

3. 0 PPM Portable 150 GPD RO+DI Filtration POQ-4B-150

This RO/DI filtration system is packaged as a complete ready to install kit.

The filtration system can be temporarily attached to the garden hose or sink and stowed away when not in use.

The manufacturer recommends this reverse osmosis system for water supplies with a TDS level of 300 ppm or less.

Some tap water supplies have over 450 ppm TDS, however.

The water output is rated at 150 gallons per day.

The POQ-4B-150 RO/DI system uses sediment, activated carbon and DI cartridges but they are not available as individual replacement parts.


  • Inexpensive budget RO/DI system.
  • Comes with 12 feet of flexible tubing for connecting incoming tap water and wastewater to the drain.
  • Works with a minimal water pressure of 35 psi.
  • Small size does not take up a lot of space.


  • No replacement cartridges are available. You have to purchase a new RO/DI filtration system when one of the filter components gets clogged.
  • The deionizing resin chamber is small and is not refillable.
  • The deionizing resin cartridge is white PVC. You will not be able to tell when the DI resin is exhausted by looking at the cartridge.
  • Brittle plastic faucet adapter.

4. LiquaGen 6-Stage Aquarium Reef Filter System (RO/DI) | 100 GPD Membrane

This RO/DI system provides six stages of purification.

A replaceable polypropylene sediment filter protects the RO membrane by removing fine filter-clogging particles of grit, rust and mineral carbonates.

Two activated carbon cartridges eliminate chlorine, chloramine, pesticides, radon and volatile organic compounds (VOCs) like gasoline.

The US-made General Electric RO membrane removes heavy metals, mineral salts, arsenic, and lead.

Twin color-changing mixed-bed deionization cartridges scavenge out any traces of nitrate, phosphate, ammonia, and metals.


  • Produces 100 gallons per day even at lower water pressure.
  • Twin activated carbon cartridges ensure complete removal of chlorine and chloramine.
  • The DI resin canisters are clear and easy to see through.
  • Twin DI cartridges ensure the filtered water is ultra-pure at all times.
  • Comes with a flush kit to remove carbon fines and prevent RO membrane clogging.
  • Pre-assembled, just connect and go!


  • 100 gallons per day may not be enough water for some aquarists.
  • Does not come with a storage tank.
  • No pressure gauge to monitor maintenance requirements.

5. iSpring 75GPD 6-Stage RO DI Water Filter

The iSpring 6-stage RO/DI water filter provides complete water purification through six individual filtration stages.

This filtration system is suitable for aquarium use and drinking water.

Sediment, mineral scale, and grit are captured in the spun polypropylene pre-filter cartridge.

The iSpring system uses a granular activated carbon (GAC) cartridge followed by a compressed block activated carbon cartridge.

The solid block carbon cartridge also acts as a particulate filter to protect the RO membrane from activated carbon dust. Dusty carbon cartridges can clog RO membranes. Both carbon filters act to remove harmful chlorine and chloramine as well as organic pollutants like herbicides, petroleum products from leaking underground fuel tanks and radon.

The TFC reverse osmosis membrane will remove dissolved minerals, nitrate, algae-promoting phosphate and silicate and metals like copper and lead. The iSpring system sends the filtered water through a coconut shell post filter as a safety factor to remove any residual chlorine that could slip through the filter system.

The last stage uses a color-changing deionization post filter. The clear DI chamber makes it easy to see when the resin needs to be changed.

The kit comes with a 3.2 gallon pressurized storage tank. The storage will allow the system to keep producing and storing water even when you are not at home.

If you need more water, a four-gallon plastic storage tank is available as an upgrade.

A helpful assembly and installation video is available here:


  • Provides complete water purification for aquariums and drinking water.
  • Uses a solid block activated carbon cartridge to capture debris.
  • Includes a storage tank.
  • The kit comes with a designer faucet suitable for mounting on the kitchen sink.
  • Replacement cartridges are available.
  • Comes with everything needed for the installation.


  • The filter system needs to be assembled.
  • No pressure gauge to monitor clogging of the filters.

My Pick

If you have a small aquarium or require a budget RO/DI system, consider the RO Buddie 4-Stage System. The filter is easy to connect to the water supply and easy to store when not in use. Unlike the 0PPM Portable 150 GPD, replacement cartridges are available.

This RO/DI system is well-suited for smaller freshwater and reef aquariums. There are only four filter stages to maintain, making filter cartridge replacement more economical.

For larger freshwater aquariums, fish breeders and reef aquariums the iSpring 75GPD 6-Stage is recommended. The iSpring is a heavy-duty RO/DI system with lots of features.

The twin activated carbon cartridges (granular and solid block) are an upgrade along with the coconut carbon post filter. The 6-Stage Reef RO/DI has two small deionization filters compared to the single large DI filter on the iSpring.

It is more convenient to change one iSpring DI cartridge than two smaller DI filters.

The iSpring also includes a storage tank and a sink dispenser. This doubles the value of this filtration system since you’ll be able to get drinking water from an attractive faucet or fill a buck with water in the sink.

If you have any questions or comments, post them below!

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