Two Little Fishies PhosBan Reactor 150
Two Little Fishies
A small upflow media reactor that gently fluidizes granular ferric oxide (GFO) so every granule contacts the water, built for up to 200 g of PhosBan on systems up to about 150 gallons.
Why it mattered
Phosphate control before GFO meant algae battles and water changes. PhosBan was among the first GFO products offered to reef aquarists, and the Reactor 150 arrived alongside it as the hardware that made the media work properly.
The upflow design matters: water enters at the bottom through a dispersion plate and lifts the granules into a slow tumble, preventing the channeling and clumping that plague media stuffed in a filter bag.
Julian Sprung's Two Little Fishies kept the design simple, cheap, and nearly unchanged for decades, and it is still sold today. The hang-on reactor became the default first reactor most keepers ever buy — for GFO, carbon, or biopellets.
Key specs
- Upflow fluidized design with dispersion plate
- Holds up to 200 g of PhosBan GFO
- One reactor per up to ~150 gal of system volume
- GFO flow rate about 20–30 gal/hr for a gentle tumble
- Hang-on-tank or in-sump placement
Keeper notes
- Keepers stress the gentle tumble: too much flow grinds GFO to dust that escapes into the tank.
- Many run a second unit for activated carbon, making the 150 a two-part media station.
- Its longevity is the reputation — decades-old units still seal and run.