The short answer
For most reef keepers, the sensible starting point is a 50–100 GPD aquarium unit with sediment, carbon, RO membrane and DI polishing. The TMC Pure 100 is a practical UK baseline if you are happy to add its DI pod; the Osmotics Ultra-Pure 100 is the more complete four-stage option. The Aqua Medic unit is an RO-only comparison, not a finished 0-TDS reef setup.
| System / checked price | Published output | Stages | Monitoring / hardware | Planning fit |
|---|---|---|---|---|
| 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 route; add DI if your reef target is 0 TDS |
| TMC Pure 100 £124.99 | up to 380 l/day | Sediment → carbon → RO membrane | Pressure gauge + flush valve | Straightforward UK aquarium unit; optional V²Pure DI pod |
| TMC Pure 100 Advanced £149.99 listed | up to 380 l/day | Sediment → carbon → RO membrane | Inline feed/permeate TDS meter | Useful monitoring upgrade; retailer status was sold out when checked |
| Osmotics Ultra-Pure 100 £158.52 | up to 380 l/day | Sediment → carbon → RO → DI | 0 ppm TDS output claim | Most complete out-of-box reef route in this comparison |
RO versus RODI
Aqua Medic describes its professional 100 as sediment filtration, carbon protection and a TFC membrane, with up to 98% rejection and roughly a 3–4:1 concentrate-to-permeate ratio. That is useful RO water, but it is not the same as a final DI-polished output. TMC’s V²Pure 100 is also a three-stage RO unit until you add the optional de-ionising pod. If a product page does not show a DI stage, do not assume it produces 0 TDS.
Pressure is the hidden buying decision
Unpumped units need adequate mains pressure. Aqua Medic’s published performance is based on specified test conditions, while TMC warns that real output falls with lower pressure and temperature. If your home has weak pressure, plan for a booster pump or choose a pumped system; buying a faster membrane without the pressure to drive it usually buys disappointment.
What to check before ordering
- Does the system include DI resin, or is it RO-only?
- Is the membrane a standard size with replacement parts available in the UK?
- Does it include a pressure gauge, flush valve, TDS meter and shut-off hardware?
- Can you route the waste line safely and collect the product water without leaks?
- Is the current listing actually in stock, and does the retailer support the exact model?
Sources and limitations
Technical claims were checked against Aqua Medic, TMC and Osmotics. Prices were checked against UK retailer listings. We have not independently measured output, rejection, noise or filter life.