At-a-glance comparison
| Decision | Dosing pump / two-part | Calcium reactor |
|---|---|---|
| Starting cost | Pump plus additives; often the lower entry cost | Reactor, CO₂ regulator, media and often a pH-control plan; higher entry cost |
| What it adds | Separate calcium and alkalinity solutions, with optional magnesium or trace products | Calcium and carbonate from dissolved media; exact output depends on reactor tuning and media |
| Control method | Calibrate pump volume and adjust daily or weekly dosing | Tune effluent flow, CO₂ bubble rate and reactor pH |
| Scaling | Add channels or larger reservoirs as demand grows | Efficient for high demand, but footprint and CO₂ logistics become part of the system |
| Main failure risks | Empty reservoir, blocked line, calibration drift or a programming error | CO₂ or pH-control error, effluent blockage, media depletion or a pump failure |
Where the cost gap appears
Current UK examples show the spread clearly: a four-channel Red Sea ReefDose 4 is listed at £329, while a small Deltec PF509 calcium reactor is listed around £378.99 before you account for CO₂ equipment and ongoing media. A Deltec Twin-Tech 1500 listing is around £1,999.99. These are product examples, not a total-cost forecast.
Which route fits a smaller reef?
For a new or lightly stocked system, a reactor is usually hard to justify before you have demonstrated sustained demand. A doser with a conservative two-part plan keeps the chemistry visible and the initial commitment smaller. As demand grows, compare the cost of bottles, pump channels and maintenance with a reactor’s CO₂ and media workflow.
Do not outsource testing
Both methods still need calcium and alkalinity checks. A reactor can deliver a steady effluent while the tank’s actual demand changes; a doser can deliver the programmed volume while a line blocks. Monitoring is the control loop in either case.
Sources and limitations
Current UK examples were checked against Red Sea ReefDose 4, Deltec PF509 and Deltec Twin-Tech 1500. We have not independently measured capacity, stability, noise or running cost.