Saltwater aquarium gear guide
For most beginners, I recommend the AquaReady Hang-on-Back Media Reactor. Nearly every beginner aquarium I recommend is an all-in-one system without a sump. A hang-on-back reactor gives you a practical place to run activated carbon or GFO without trying to cram a full-size canister into a tiny rear filtration chamber.
What does an aquarium media reactor actually do?
This video gives you the foundation before you compare products. It explains how a reactor pushes aquarium water through media so the entire surface is used more consistently than it would be inside a passive media bag.
- See how water moves through the reactor chamber.
- Understand when activated carbon or GFO may be useful.
- Learn why placement and flow control matter before you buy.
AquaReady Hang-on-Back Media Reactor
It hangs directly on the aquarium, so it solves the biggest installation problem beginners face: no sump and very little room behind an all-in-one filtration wall.
Best for: Beginner all-in-one aquariums that need a practical reactor for carbon or GFO.
Know before you buy: The reactor does not include a feed pump or tubing.
Five saltwater aquarium media reactors compared
The most important difference is not appearance or maximum media capacity. It is where the reactor can realistically live in your system. Choose the installation style first, then choose the size and maintenance design.
| Media reactor | My pick for | Placement | Published capacity | Pump | Main trade-off |
|---|---|---|---|---|---|
| AquaReady HOB | Best beginner AIO option | Hang on back | About 4.2 cups | Not included | You must add tubing and a controllable feed pump |
| BRS Mini | Compact sump or cabinet installation | HOB, sump, or wall mounted | Up to 3/4 cup carbon | Optional | Still needs plumbing and a place for the pump |
| AquaReady Sigma 2 | Easiest media changes | In sump | 2 cups carbon or 1.5 cups GFO | Included | Requires a sump and costs more |
| BRS Single | Best full-size value | Sump, stand, or wall | 3 cups carbon or 2 cups GFO | Optional | Large for a beginner AIO |
| BRS Deluxe | Premium full-size BRS option | Sump or wall mounted | 3 cups carbon or 2 cups GFO | Optional | More reactor than most beginners need |
Do you need a media reactor at all?
A media bag in a high-flow area may be enough.
A reactor forces aquarium water through the media, which creates more consistent contact than simply dropping a bag into a chamber. That can make activated carbon or GFO work more efficiently, but it also adds a pump, tubing, maintenance, and another possible leak point.
If your tank is clear, your phosphate is under control, and a media bag is doing the job, you do not need to add a reactor just because one exists. Buy one when you have a specific reason to improve how water moves through the media.
How I chose these media reactors
I ranked them for the beginner systems I actually recommend, not for a hypothetical aquarium room with unlimited sump space. Installation practicality came first, followed by how easy the reactor is to service, how precisely the flow can be adjusted, and whether its capacity makes sense for the tank.
I have not used this exact model, but I have used AquaReady equipment and similar HOB reactors. Its placement solves the main problem for tanks without sumps.
I have personally used it. It uses the familiar BRS cartridge design in a smaller body that is more appropriate for modest media amounts.
I have used it. The removable chamber locks into the pump base, so media changes do not require pulling out and disconnecting the pump.
I have used it. It is straightforward, durable, and less expensive than the Deluxe while holding the same published maximum media amounts.
I have used it. It adds a slimmer profile, integrated fittings, a pressure-release valve, and a cleaner finish—but most beginner tanks do not need it.
1. AquaReady Hang-on-Back Media Reactor
My experience: I have not personally used this exact reactor. I have used AquaReady products and comparable hang-on-back reactors, and the installation style is the best match for the all-in-one aquariums I recommend.
The sensible way to add a reactor without a sump
Approximately 4.2 cups
12.5-inch minimum height; up to 3/4-inch rim
- The up-flow design works with activated carbon, GFO, or biopellets.
- Adjustable 1/2-inch hose barbs keep the inlet and outlet organized.
- The current listing recommends about 150 GPH for carbon or GFO.
- A controllable feed pump is the easiest way to tune the media correctly.
What to know first: Only the reactor is included. You must add flexible tubing and a feed pump, and you need enough clearance behind the aquarium for the body and plumbing.
My verdict: This is the reactor I would start with for a beginner AIO. It gives carbon or GFO consistent flow without forcing a full-size reactor into a system that was never designed to hold one.
Watch the AquaReady hang-on-back media reactor walkthrough:
2. BRS GFO & Carbon Mini Reactor
My experience: I have personally owned and used this reactor. It is the smallest version of the familiar BRS canister design.
Smaller capacity for smaller systems
9 x 8 x 5.5 inches
3/4 cup carbon or 1/2 cup carbon/GFO mix
- The refillable cartridge makes it easy to see and contain the media.
- A ball valve provides precise flow control.
- The reactor-only and pump-package versions are both available.
- It can be mounted in a sump, on a wall, or in a suitable HOB arrangement.
What to know first: “Mini” does not mean it will fit inside a narrow all-in-one rear chamber. You still need room for the canister, tubing, and feed pump.
My verdict: This is my second choice because its capacity is appropriate for many beginner tanks. Buy it when you have a sump, a roomy filtration area, or a clean cabinet installation plan.
3. AquaReady Sigma 2 Media Reactor
My experience: I have used this reactor. Its removable chamber and fixed pump base genuinely make routine media changes easier.
Leave the pump in place and remove only the canister
5.12 x 5.51 inches
Sicce Syncra 0.5, 185 GPH
- The chamber twists to lock or unlock from the docking base.
- The pump and power cord can remain in the sump during maintenance.
- Flow can be adjusted at the pump and by twisting the canister.
- Published capacity is 2 cups carbon or 1.5 cups GFO.
What to know first: This is an in-sump reactor. The clever base does not solve the placement problem if your aquarium has no sump.
My verdict: If you have a sump and hate disconnecting pumps whenever you replace media, this is the most convenient design on the list.
Watch the AquaReady Sigma 2 media reactor walkthrough:
4. BRS GFO & Carbon Reactor — Single
My experience: I have personally owned and used this reactor. It is the sensible middle ground in the BRS lineup.
The straightforward full-size BRS reactor
14 x 8.5 x 5.5 inches
3 cups carbon or 2 cups GFO
- Heavy-duty canister construction is simple and durable.
- The refillable cartridge, wrench, tubing, and flow valve are included.
- An optional package adds a Sicce Syncra 1.5 feed pump.
- It can be mounted in a sump, inside a stand, or on a wall.
What to know first: It takes more space than the Mini and is awkward for most beginner AIO aquariums. External plumbing can work, but it adds tubing runs and head pressure.
My verdict: Choose the Single when you need full-size capacity but do not care about the Deluxe model’s appearance and refinements.
Watch the BRS standard and Deluxe media reactor walkthrough:
5. BRS GFO & Carbon Reactor — Deluxe
My experience: I have personally owned and used the BRS Deluxe reactor. It is an excellent reactor, but it is not the one that makes the most sense for most beginner aquariums.
A cleaner, slimmer version of the full-size BRS design
13 x 6 x 5 inches
3 cups carbon or 2 cups GFO
- The slim black body looks cleaner than the standard canister.
- Integrated push-connect fittings reduce potential leak points.
- A pressure-release valve helps remove trapped air.
- An optional package includes a Sicce Syncra 1.5 pump.
What to know first: This still belongs in a sump or deliberate wall-mounted installation. The polished construction does not make it a natural fit for a small AIO rear chamber.
My verdict: It may be the nicest traditional reactor here, but beginners should not confuse “best-built” with “best for my tank.” Buy it when you have the installation space and want the upgraded BRS design.
Carbon and GFO need different flow
Carbon should stay contained. GFO should only tumble gently.
Activated carbon can grind itself into dust if it is allowed to tumble aggressively. Hold it between the reactor pads and run enough flow to move water through it without letting the media churn.
GFO should move slightly at the surface so it does not clump into a solid mass, but more flow is not better. Start low and increase slowly. GFO can lower phosphate quickly, so use the manufacturer’s recommended amount and monitor the aquarium rather than filling the reactor simply because there is empty space.
Which aquarium media reactor should you buy?
Start with the physical installation. If you have a beginner AIO without a sump, the AquaReady HOB is the obvious place to begin. If you have a sump, choose based on capacity and how much you value easier maintenance.
| Reactor | Best for | Avoid it when | Pump included? | Maintenance | Price level | Current option |
|---|---|---|---|---|---|---|
| AquaReady HOB | Beginner AIO without a sump | Your tank is too short, has a thick rim, or lacks rear clearance | No | Simple HOB access | Midrange plus pump | Check BRS price |
| BRS Mini | Smaller media amounts with suitable mounting space | You expect “mini” to fit inside a narrow AIO chamber | Optional package | Remove canister and cartridge | Budget | Check BRS price |
| AquaReady Sigma 2 | Sump owners who prioritize easy media changes | You do not have a sump | Yes | Twist canister off fixed pump base | Premium | Check BRS price |
| BRS Single | Full-size capacity at a practical price | Space is tight | Optional package | Traditional canister service | Budget to midrange | Check BRS price |
| BRS Deluxe | Premium full-size BRS installation | You only need a small amount of media | Optional package | Traditional canister with pressure release | Midrange | Check BRS price |
Product dimensions, included accessories, prices, and availability can change. Confirm the current listing and measure your installation area before ordering.
Saltwater aquarium media reactor FAQ
What does a media reactor do in a saltwater aquarium?
It forces water through filtration media instead of letting water flow around a media bag. This improves contact with activated carbon, GFO, or another compatible media.
Can I use carbon and GFO in the same reactor?
Yes, if the reactor and media instructions allow it, but the two materials prefer different flow. Carbon should not tumble, while GFO should move only gently at the surface. Mixing them also means replacing both on the same schedule.
Do I need a sump for a media reactor?
No. A hang-on-back reactor is made for systems without a sump. Traditional canister and in-sump reactors are usually easier and cleaner to install when a sump or roomy cabinet is available.
Does the AquaReady HOB reactor include a pump?
No. The current BRS listing includes the reactor but not the feed pump or tubing. AquaReady recommends a controllable pump, with roughly 150 GPH listed for carbon or GFO before adjustment for the actual amount of media.
How often should I replace carbon or GFO?
Follow the media manufacturer’s directions and the reason you are running it. Carbon replacement depends on the organic load and desired clarity. GFO replacement should be guided by phosphate testing rather than a fixed calendar alone.
Can a media reactor lower phosphate too quickly?
Yes. Too much fresh GFO can change phosphate rapidly. Start with the recommended amount, adjust flow gently, and monitor the tank instead of filling the reactor to capacity.
Finish the filtration plan
Once you know which reactor fits your system, visit the Saltwater Aquarium Gear Guides for the rest of the equipment, then use the Maintenance Guides to build media changes into a routine you will actually follow.
