Media Reactor Guide

How a media reactor forces water through chemical filter media such as carbon, GFO or biopellets, the fluidized design, and how to run one.

What it is

A media reactor is a contained chamber that forces aquarium water through chemical filter media such as activated carbon, granular ferric oxide (GFO) or biopellets. It is used for targeted treatment, maximizing the contact between the water and a specific medium.

How it works

Water is driven through the media held inside the chamber rather than allowed to flow passively around it. In a fluidized design, a flow-adjustable pump positioned below the chamber keeps the media tumbling while treated water overflows out the top and returns to the tank or sump. Tumbling ensures every part of the media gets a fairly equal amount of exposure to the incoming water.

How the media act

Activated carbon removes dissolved organic compounds and other impurities by adsorption onto its porous surface; it becomes saturated and is replaced rather than left in place. GFO is used to bind phosphate, while biopellets supply a carbon source that supports bacteria which consume nitrate and phosphate. Each medium targets a different contaminant, which is why a reactor is matched to a specific goal.

Why fluidize the media

Pellet-specific reactors were designed to keep the media moving so it does not clump. Clumping can allow hydrogen sulfide to accumulate, which could poison the tank. Biopellets are run with enough flow to tumble fully, whereas GFO is run with gentler flow so only the top of the bed slightly tumbles rather than rolling vigorously.

Choosing and sizing

The reactor is matched to the medium it will hold and to the system's water volume and nutrient load. Flow is adjustable so it can be tuned to the medium: a strong rolling boil suits biopellets, while finer GFO needs a slower flow to avoid grinding. Running incompatible media together is avoided; for example, GFO and biopellets are not run in the same chamber.

Maintenance

Spent media is replaced on a schedule appropriate to each type, since saturated carbon can re-release adsorbed contents and exhausted GFO stops binding phosphate. The pump, fittings and chamber are checked for clogging or channeling, and flow is re-tuned after a media change so the bed tumbles correctly.