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QUICK VERDICT
Our picks at a glance
The TMC Pure 100 is a sensible UK choice once you add a DI pod, while the Osmotics Ultra-Pure 100 is the most complete four-stage reef unit here.
Best compact RO unit
Aqua Medic easy line professional 100
£106.63
Compact RO only; add a DI stage if you want 0 TDS for your reef
Search Amazon UK ↗Best all-round UK pick
TMC Pure 100
£124.99
A straightforward UK aquarium unit; DI pod available separately
Search Amazon UK ↗Best complete RODI unit
Osmotics Ultra-Pure 100
£158.52
The most complete reef-ready unit out of the box here
Search Amazon UK ↗OUR PICKS IN DETAIL
Who each one is really for
Best compact RO unit
Aqua Medic easy line professional 100
Best for
Compact RO only; add a DI stage if you want 0 TDS for your reef
Why we picked it
approx. 300 l/day; Sediment → carbon → RO membrane.
The catch
No DI or built-in TDS meter
Only if you’ll add a DI stage, so your water reliably reaches reef quality.
Search Amazon UK ↗Best all-round UK pick
TMC Pure 100
Best for
A straightforward UK aquarium unit; DI pod available separately
Why we picked it
up to 380 l/day; Sediment → carbon → RO membrane.
The catch
Pressure gauge + flush valve
Yes, as a well-known aquarium unit. Budget separately for the optional DI stage.
Search Amazon UK ↗Best complete RODI unit
Osmotics Ultra-Pure 100
Best for
The most complete reef-ready unit out of the box here
Why we picked it
up to 380 l/day; Sediment → carbon → RO → DI.
The catch
0 ppm TDS output claim
Yes, if having every stage from RO to DI in the box is worth the higher price.
Search Amazon UK ↗HOW WE RESEARCHED
How we chose
We compared manuals, manufacturer specifications, current UK retailer listings, running requirements, ownership costs and support. This is desk research, not hands-on testing, and where something is uncertain we say so.
- RO only, or full RODI
- Output at realistic water pressure
- TDS monitoring
- Waste water and replacement costs
- UK fittings, price and support
The short answer
For most reef keepers, the sensible starting point is a 50–100 GPD aquarium unit with sediment and carbon filters, an RO membrane and a DI stage. The TMC Pure 100 is a sensible UK choice if you’re happy to add its DI pod; the Osmotics Ultra-Pure 100 is the more complete four-stage option. The Aqua Medic is RO only, so on its own it won’t give you 0 TDS reef water.
| Unit / checked price | Published output | Stages | Monitoring / hardware | Best for |
|---|---|---|---|---|
| Aqua Medic easy line professional 100 £106.63 | approx. 300 l/day | Sediment → carbon → RO membrane | No DI or built-in TDS meter | Compact RO only; add a DI stage if you want 0 TDS for your reef |
| TMC Pure 100 £124.99 | up to 380 l/day | Sediment → carbon → RO membrane | Pressure gauge + flush valve | A straightforward UK aquarium unit; DI pod available separately |
| TMC Pure 100 Advanced £149.99 listed | up to 380 l/day | Sediment → carbon → RO membrane | Inline feed/permeate TDS meter | Handy built-in monitoring; sold out at the retailer when we checked |
| Osmotics Ultra-Pure 100 £158.52 | up to 380 l/day | Sediment → carbon → RO → DI | 0 ppm TDS output claim | The most complete reef-ready unit out of the box here |
RO vs RODI: what’s the difference?
Aqua Medic describes its professional 100 as a sediment filter, a carbon filter and a TFC membrane, with up to 98% rejection and about 3–4 litres of waste for every litre of clean water. That’s useful RO water, but it isn’t the same as water finished with a DI stage. TMC’s V²Pure 100 is also a three-stage RO unit until you add the optional DI pod. If a product page doesn’t show a DI stage, don’t assume it makes 0 TDS water.
Water pressure is the hidden decision
Units without a pump rely on good mains pressure. Aqua Medic’s figures come from specific test conditions, and TMC warns that real output drops with lower pressure and colder water. If your home has weak pressure, plan for a booster pump or buy a pumped system. A faster membrane without the pressure to drive it usually just leads to disappointment.
Five things to check before you order
- Does it include DI resin, or is it RO only?
- Is the membrane a standard size, with replacements available in the UK?
- Does it come with a pressure gauge, flush valve, TDS meter and automatic shut-off?
- Can you route the waste line safely and collect the clean water without risking leaks?
- Is it actually in stock, and does the retailer support that exact model?
Sources and limits
We checked technical claims against Aqua Medic, TMC and Osmotics. Prices come from UK retailer listings. We haven’t measured output, rejection, noise or filter life ourselves.
WHICH ONE FITS YOU?
Choose your unit based on your tap water
Typical mains water and a small reef
A compact three- or four-stage unit may be plenty if your water pressure and tap-water TDS are reasonable. A proper DI stage is worth having if you want 0 TDS water for your reef.
Hard water or high tap-water TDS
Membrane rejection and the capacity of the sediment and carbon filters matter more. Check your water pressure and your supplier’s water report before blaming a unit for slow output or resin that runs out fast.
Low pressure, or lots of water needed
A booster pump and a higher-capacity membrane can cut waiting time and improve rejection, if they’re matched properly. The waste ratio and safe unattended running become more important too.
HOW TO CHOOSE
What to check before you buy
Check your pressure and water temperature
Membrane ratings come from specific test conditions. Cold UK tap water and low pressure can cut output significantly, so the litres-per-day figure isn’t a promise.
RO isn’t the same as RODI
An RO unit removes most dissolved solids; a DI stage polishes out what’s left. Check whether the package actually includes the resin, its housing and a way to measure the final TDS.
Check it handles your water treatment
The carbon filters and how long water spends in them need to suit the disinfectant your supplier uses. Check your water supplier’s information and the filter maker’s limits.
Collect the water safely
Use a float valve and automatic shut-off, ideally with a leak plan that suits the room. Never leave a unit filling unattended without a tested overflow safeguard.
RUNNING COSTS
What it costs after you buy it
Pre-filters and resin
Sediment and carbon filters and DI resin all need replacing. How long they last depends on your water and how much you make, so pressure and TDS readings are a better guide than the calendar.
Waste water
Note how much waste it produces for each litre of clean water in your conditions. You can sometimes reuse waste water around the house, but it isn’t purified drinking water.
Meters and calibration
Inline TDS meters are convenient; a handheld meter lets you double-check them. A pressure gauge helps you spot a blocked pre-filter or poor feed pressure.
ALTERNATIVES
Other options worth a look
Add a booster pump
If your water pressure is below what the membrane needs, boosting it may do more than buying a bigger-rated filter.
Buy RO water
Buying water from a shop avoids the equipment cost for a very small tank, but factor in transport, storage, consistency and the long-term cost.
HOW WE RANK
What it takes to make our list
It has to fit
Before we compare features, we rule out anything that doesn’t suit the tank, the installation or the job. A famous name can’t win if its size, operating range, connections or controls make it a poor match.
Claims need context
A spec sheet tells you what a product is designed to do, not how it will behave in your reef. So we look at the conditions behind every capacity, flow, output and accuracy claim, and flag any conclusion that’s an informed judgement rather than a measurement.
Every pick shows its catch
Each product’s main drawback sits right next to its biggest strength. We don’t hide a support worry, a missing accessory, a vague rating or a pricey ecosystem just because the product is the best choice for one type of buyer.
UK ownership breaks ties
Availability, what’s actually in the box, consumables, spares, UK plugs and the warranty route all count. When two products do the job equally well, the one that’s easier to own in the UK gets the stronger recommendation.
We don’t publish a one-size-fits-all league table. Each award answers a different buying situation, and the final verdict explains which trade-off we’d make. If your tank, budget or routine doesn’t match any of them, use the checks above to build your own shortlist rather than just buying the top badge.
COMMON QUESTIONS
Frequently asked questions
Does a reef tank need RODI water?
It’s the most controllable starting point, because it removes the variable contents of tap water before you add salt. How much it helps depends on your tap water, but it takes the guesswork out.
Why is my RODI unit so slow?
Cold water, low pressure, a clogged pre-filter or the conditions behind the membrane’s rating can all slow it down. Check your pressure and water temperature before replacing parts.
When should I replace DI resin?
Monitor the final TDS and follow the maker’s advice. Replace it before it’s exhausted and lets unwanted ions through; a colour change alone isn’t always enough of a warning.
BEFORE YOU ORDER
Three checks before you pay
Confirm the exact model
Shop listings often mix up generations, sizes and regional versions. Check the full model code, UK plug, included accessories and who handles the warranty against the manufacturer’s own details. Save the product page and spec sheet in case the listing changes.
Price everything it needs
Add the mount, controller, adapters, consumables, test kit and likely replacement parts you’ll need to run it. Compare that first-year total, not the headline price, and keep a little extra for plumbing, cable tidying or the fitting you forgot.
Measure twice at home
Measure your tank, cabinet, sump chamber, glass, sockets and the space you need to service it. Then write down the one job this kit has to do, and how you’ll know it’s working. If it won’t fit, or you can’t tell whether it’s doing its job, it’s the wrong choice.
Prices and stock change quickly. Every price here is a dated UK snapshot, so confirm the total at checkout and the returns terms, and don’t swap in a similarly named model without running these checks again.
OUR VERDICT
Buy the right filter stages, not the biggest output claim
Start with your tap-water TDS, its disinfectant, your water pressure and temperature, and how much water you need each week. Choose stages and capacity from those, then budget for monitoring, replacement filters and a safe way to collect the water.
Set reminders in the free Reef Companion to check your TDS and replace each stage, so a tired filter never slips past you.