Best RO/DI systems to save you time and money in 2021!

by George Mavrakis on December 18, 2021

RO/DI units are a must-have for reef hobbyists old and new. These systems are essential for properly maintaining any saltwater aquarium containing sensitive corals or invertebrates. Don’t make the terrible decision to use dechlorinated tap water instead of RO/DI water in your tank! Read more to find out why you should buy an RO/DI machine (if you haven’t already)!


What is RO/DI water and what makes it so special?

RO/DI (or RODI) stands for Reverse Osmosis and Deionization. RO/DI water is produced by running tap water through an RO/DI unit in order to remove the total amount of dissolved solids in the water. These solids include elements like nitrates, phosphates, and chlorine, as well as various metals like copper and lead that enter the water due to the metal plumbing found in most houses.

The result is RO/DI water with a level of 0 TDS (Total Dissolved Solids), which is the best possible water for your saltwater tank. It is essential that reef-keepers use 0 TDS water because the elements that are filtered out in the RO/DI process are not found in natural reefs. Not only are these impurities unnatural, but they act as food for algae! This is why using tap water (even dechlorinated tap water) will contribute to problems such as green hair algae, cyanobacteria, and other issues in your tank. (Dechlorinated tap water might be okay for freshwater tanks, but it’s not a viable solution for saltwater coral reef tanks.)


What is an RO/DI system?

An RO/DI system is a 3-5 stage all-in-one filter that purifies tap water and produces 0 TDS water. It removes mobile charged ions such as salts, metals, and other materials found in tap water that can lead to algae blooms and a number of other problems in aquariums.


Why buy an RO/DI system for an aquarium?

An RO/DI unit is an excellent choice for both the professional aquarium keeper and aquarium hobbyist because it allows for maximum quality assurance. With an RO/DI system, you’re in control of changing the filters and making sure the water is always coming out at 0 TDS. Due to this, you will naturally find yourself doing more water changes, which will automatically lead to better quality water in your tank.

You will also be able to make perfect quality water without even leaving the house! There is no more need to buy RO/DI water or expensive fresh saltwater from your aquarium store, since you will always have what you need, right at home. (This can really come in handy in an emergency!)

Plus, buying an RO/DI machine will save you a lot of time and money in the long run. Not only will it prevent you from troublesome problems like algal blooms, but it will save you from having to keep continually buying RO/DI water from your aquarium store. A quality machine will cost a bit no matter what (at least around $150 for a good one), but the investment is definitely worth it as it will easily save you money over time!


Do I really need an RO/DI unit?

Yes! Even if you are buying RO/DI water from your local fish store or have a small tank, you need an RO/DI system for your saltwater aquarium! Often local fish stores will sell fresh saltwater with a TDS level of 3-5, which can still cause some issues in your tank. Give yourself the peace of mind and buy an RO/DI filter, knowing that you are using true 0 TDS water!

Additionally, choosing a filter generally requires extensive knowledge of what pets you want to keep, but an RO/DI system will work with reef, freshwater, and marine aquariums. Tap water will only work for some fish, but RO/DI water will work for most anything! Thinking of getting another tank? Get an RO/DI unit! It will cover all your bases.

Even for freshwater fish, having an RO/DI unit can be very helpful. The mineral concentrations and pH of tap water may vary from home to home and may not be suitable for your fish. And in some places, you risk exposing soft water fish to hard water.

There isn’t really a solution other than buying RO/DI water from your local fish store or buying an RO/DI machine!


Now that you know why it is so essential to use 0 TDS water in your saltwater reef tank, AND buy your own RO/DI unit, here is a list of the top RO/DI systems for 2021!



Top RO/DI Units for Aquariums [2021]

1. AL Aquatic Life 100 GPD 4 Stage RODI unit - $124.99

rodi machine

The Aquatic Life twist-in 100 gpd (gallon per day) 4-stage reverse osmosis deionization system is a very compact water purification solution that efficiently combines reverse osmosis and deionization technology with quick and easy to change twist-in replacement filter cartridges. The new twist-in media cartridge design makes filter changes simple, easy and clean – no tools required and no mess! The twist-in cartridges can be easily changed in seconds with just a quarter-turn and without contact with used filter material, and the supply water to the unit does not have to be turned off to replace any cartridge.

Dimensions: 13” wide x 4” deep x 13” high. Weight: 7 lbs.


 2. Melev’s Reef 100 GPD 5 Stage RODI unit - $199.00

rodi water unit

This 5 stage, 100 gallon per day RODI unit from Melev’s Reef is perfect for beginners. Fully assembled and ready to use out of the box, this RODI machine comes with a 5 micron sediment filter, two 5 micron carbon blocks, a color changing DI resin cartridge, filter housing wrench, clear acrylic housings for viewing the cartridge, and an automatic shutoff valve. Additionally, on, there are easy to follow instructions that any beginner can understand. Plus, the maker, Mark Levinson, is easy to contact if any problems should arise. This RODI system can be used for drinking water as well as reef water and comes with a 1 year warranty.


 3. Liqua 5-Stage Reverse Osmosis and Deionization RO/DI - $154.99

ro di water unit reverse osmosis deionized water reef tanks

LiquaGen's 5-stage RO/DI unit is an excellent option for first time reefers who are on a relatively clean city water supply with low chlorine levels. The 5-stage unit is designed primarily for reefers but can be used for fresh water or salt water aquarium enthusiasts and a wide array of applications where ultra-pure zero TDS is needed. The 5-Stage unit is built on one frame (making it portable) and does not require permeant installation, modification, or drilling. Installation of this unit should not take more than 5 minutes!


 4. AquaFX Barracuda 100 GPD Glacial RO/DI System

ro di water filtration machine

Meet the Traditional Barracuda's cool cousin. The Barracuda Glacial comes standard with an automatic shutoff, quick connect check valve, manual flush kit, pressure gauge, inline TDS meter, AquaFX TFC Membrane(s), AquaFX carbon block filter, AquaFX 1 micron sediment filter, and a black pure aluminum bracket. Made in the USA, AquaFX is proud to have Barracuda recognized by for being #1 pick for RO/DI's within the industry. The AquaFX Barracuda is offered in several flow rates from 50 GPD to 300 GPD (Gallons per Day). This unit also allows you to select the carbon your system uses, giving you the ability to deal with disinfectants such as Chloramine or even traditional Chlorine. The Barracuda has great appeal for every reefkeeper, from the weekend hobbyist to professional service companies. 


For more information about RODI water and filtration systems, check out CoralFish12g on YouTube: