Updated July 2026
For a saltwater aquarium, the water you start with matters as much as the salt you mix into it. A dependable reverse-osmosis/deionization system removes the variable chemistry in tap water and gives you a repeatable starting point for water changes and top-off water.
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A complete RO/DI system normally uses a sediment filter, one or more carbon blocks, an RO membrane, and DI resin. The sediment stage protects the carbon, the carbon protects the membrane from chlorine or chloramine, the membrane removes most dissolved material, and the DI stage polishes the remaining ions toward zero TDS.
Before choosing a system, check four things: your utility’s disinfectant, incoming water pressure, source-water TDS, and how many gallons you need each week. Chloramine can justify additional carbon capacity, while low pressure can reduce membrane production and rejection performance. A handheld TDS meter helps verify source, RO-membrane, and final product water instead of relying on time alone.
RO-only water is better than untreated tap water, but reef tanks benefit from the final DI stage because it captures material that passes through the membrane. The AquaReady 3-stage RO system remains a budget option, and you can add a DI canister later.
Plan for safe installation too: use a shutoff strategy you understand, secure tubing fully, keep electrical connections away from possible leaks, and never leave a filling container unattended until you know the system’s production rate. For the broader routine, see my guides to doing a water change and recommended saltwater parameters.
Choosing the right RODI filter really depends on a few things. Your water source, water pressure, the amount of chlorine/chloramine, and how many gallons you need. To make life easy, if you just don’t want to deal with it, buy the first one below on the list. It will get the job done.
1. BRS 4-Stage Value Plus 75GPD
This isn’t the cheapest, but it is not anywhere near the most expensive. This is your basic 4-stage RO/DI filter, with a few add-ons that while not necessary, will help you decide when it’s time to change out your filters, and also let you know if you need to increase water pressure.
The dual inline TDS meter means you can read the quality of your water in two separate places. That means the first check right after the carbon filter will let you know when it’s time to change out the carbon block, and then the TDS check after the RO membrane will let you know when it’s time to switch out the membrane.
The water pressure gauge will not only tell you if your household water pressure is below 50 and thus not optimal for filtration, but as time goes by and you notice the water pressure start to get lower and lower, that likely means that your sediment filter is clogged and needs to be replaced. But hopefully the nasty brown color would have been your first clue.
Bulk Reef Supply has definitely cornered the market on these devices, and what’s nice is that each unit is completely upgradable. If you need more carbon blocks, just pick up an extra canister and daisy chain it in. If you want to waste less water and double your clean water output, then attach a second RO membrane to the first.
Or, if you don’t really care, but rather you just want good water for your animals, then get this filter and forget about it… At least for the first year… until it’s time to change out the media!
2. AquaReady 3-Stage RO System 75 GPD
Alright, this system isn’t perfect, but if you are really trying to keep the price down and do right by your pets, then this one is the way to go. It’s not an RODI filter since it lacks the DI resin container, but I made a video of this one for the company and tested it myself and sure enough, it reduced TDS by over 96%, which to be honest is pretty dang good. Sure, we would like to see 100% reduction, but this is better than just using tap water.
No fancy sensors or pressure gauge, but it’s a solidly built unit for a good price. And just like all of the other filters, you can upgrade easily by just adding more canisters. So definitely a good place to start.
3. BRS 4-Stage Value RODI 75 GPD
This is the exact same as #1 on the list, except without the fancy inline TDS meter and pressure gauge. You can save a few bucks with this one, which is especially useful if you know you have strong water pressure in your home. I have been using this one with an added pressure gauge for years now. I’ve added another two canisters of DI resin, and since I store it outside, the inline TDS meter has long since crapped out on me. But, I do still check the pressure gauge every time I use it, and thankfully it always overs just above 60PSI.
A fantastic starter unit that will last a lifetime, and definitely a huge upgrade over the 3-stage AquaReady RO unit.
4. BRS 5-Stage Premium Plus 150 GPD Water Saver
Alright, we are moving on to the big girls here, the 5-stage system. Now, if you are a counting person like me, you may have noticed that there are actually 6 stages in this unit. Well my good buddy, you are correct. Why they have adopted this naming convention I’ll never understand, but as I understand it, a 4-stage unit is any unit, regardless of the actual number, that has the 3 canisters plus RO membrane (like the left hand portion of this filter). A 5-stage filter adds a single extra unit to it, usually a DI resin canister. A 6-stage unit adds two additional canisters… And a 7-stage unit, you guessed it, adds three.
Hopefully that will make you feel a bit less overhwlmed if you decide to actually shop the BRS RODI filter landing page here.
So who would need this beast of a filter? A few specific incidents come to mind:
- If you need a lot of water made each day, the dual 75 GPD RO membranes will double the output.
- If you have heavily chlorinated water, it is really helpful to have two carbon chambers, as that will be the primary means of getting chlorine out of the water.
- And if all of the above is true, plus you want to cut down on waste water, the dual RO membrane cuts waste water by about half.
5. BRS 6-Stage Deluxe Plus 150 GPD Water Saver
Alright, the last RODI system on our list is the biggest and baddest… the 6-stage. Okay, there is a 7-stage available, but let’s not go too crazy here.
If you just want the cleanest water possible, made as quickly as possible, and as environmentally friendly as possible, this is the one for you. While it comes with two carbon blocks and two DI resin containers, you can swap out the media to suit your needs. For example if you have a ton of dirt in your water, maybe you remove the first carbon block and add in a second sediment filter.
This is the premium version which means it comes with the dual inline TDS meter and pressure gauge.
