Gear
RO/DI units: what reef keepers commonly use
Filters that turn tap water into pure water for top-off and salt mixing. Below are 3 items we see often, each with our honest note and where to view it in the UK and the US.
We sell nothing and earn nothing from these links. Prices are as each retailer's page showed them on the date checked, and they change. How this guide works
Listings checked . How we check
What should you look for in RO/DI units?
- A DI resin stage to take the reading to zero, and a TDS meter to tell you when it is spent.
- Enough mains water pressure for the membrane. Output drops sharply on low pressure.
- Running costs: replacement cartridges, and the waste water the membrane sends to drain.
Commonly used RO/DI units
Specs are as published on the listed pages. Where the US and UK pages give different figures, we show both.
BRS 4 Stage Value RO/DI
Brand: Bulk Reef Supply
Our note. A basic four-stage RO/DI unit that makes zero-TDS water for top-off and salt mixing. Sold in the US only, and you should add a TDS meter to know when filters are spent.
Key specs
- 75 GPD
- Sediment, carbon block, membrane, DI resin
- 99% rejection; 3:1 waste ratio
- Needs 50 to 80 psi
UK listing
Not available in this region. We found no UK listing we could check on .
US listing
Bulk Reef Supply (US): opens the retailer's page for BRS 4 Stage Value RO/DI in the United States- Price as shown
- US$179.99 (75 GPD)
- Checked
Finest Filters 75gpd 4 Stage RO Unit
Brand: Finest Filters
Our note. A low-cost UK four-stage RO unit with DI resin, supplied with a self-piercing feed valve for copper pipe. Waste water is high, and output falls on low mains pressure.
Key specs
- 75 GPD membrane
- Sediment, carbon block, membrane, DI resin
- Flush valve and flow restrictor fitted
UK listing
Kraken Corals (UK): opens the retailer's page for Finest Filters 75gpd 4 Stage RO Unit in the United Kingdom- Price as shown
- £89.99
- Checked
US listing
Not available in this region. We found no US listing we could check on .
Aquatic Life RO Buddie 4-Stage
Brand: Aquatic Life
Our note. A compact wall-mounted RO/DI unit with colour-changing resin, sold in both countries. Its output is slow and its carbon stage does not deal with chloramine.
Key specs
- 50 GPD
- Four stages including colour-changing DI
UK listing
Amazon UK (UK): opens the retailer's page for Aquatic Life RO Buddie 4-Stage in the United Kingdom- Price as shown
- Price not shown on the page when we checked
- Checked
US listing
Amazon.com (US): opens the retailer's page for Aquatic Life RO Buddie 4-Stage in the United States- Price as shown
- Price not shown on the page when we checked
- Checked