Saltwater Aquarium Blog

Choosing the Best Aquarium Reactor Media

Everyone loves a clean saltwater aquarium. But crystal-clear views through the glass don’t happen by magic. You need special filters such as aquarium reactor media to get the job done. Otherwise, you face an uphill battle with potential toxins, wastes, and thriving algae. (To say nothing of the potential health hazards your fish and invertebrates will cope with as a result) When you start looking at reactor media, though, you’ll find multiple options. How to know which works best? That’s where this article comes in handy.

Table of Contents: Aquarium Reactor Media

Aquarium reactor media come in different forms and types. You need a thorough understanding of how each one works to clear a tank, as well as the risks involved. As such, it’s best if you go through this entire post to gain a thorough understanding of how to work with these filters. If you’re already set on a particular media type, though, these links will allow you to drop down and pick the one that works best for you.

What is Aquarium Reactor Media?

“Reactor” conjures plenty of different thoughts to mind. However, if you’re hoping to generate power or conduct science experiments when you add an aquarium reactor to your aquarium, you’re out of luck. The equipment isn’t that fancy – or even that technical. And neither’s the aquarium reactor media that sits inside. The reactor’s job is to improve filtration efficiency. And it does that through the reactor media.

Aquarium reactor media increases the amount of surface area the water encounters. This means more contact time and a better chance to remove unwanted waste compounds or impurities. Similar to that deep sand bed you added to the bottom of your tank, the nooks and crannies of your media boost the reactor’s ability to work. Aquarium reactor media sit inside the container (held in place by sponges) and filter out the things that cloud and discolor your water. You don’t even need a hefty reactor, either (we’ll go over that).

Hobbyists have plenty of aquarium reactor media to choose from. And that’s often where problems can set in. Because no two media are alike.

How to Decide What Aquarium Reactor Media You Need?

If there were only one type of aquarium reactor media, people wouldn’t struggle to choose one. You’d find the most respected brand (or the one that fits your budget) and be on your way. No decision to make (not really, anyway). But when you walk down the aisles at your local fish store or scroll through an online supply, you’ll see different types. The media feature different sizes and names. And if you’re not sure what everything means, you can find yourself in a struggle.

That’s where some key questions can come in and help you narrow your search.

Do You Have to Pick ONE?

The first thing to consider is whether or not you need to make a decision in the first place. And the answer’s NO.

Plenty of people plumb reactors in a series, utilizing multiple aquarium reactor media, so they purify the tank water utilizing more than one approach. This provides the best of, well, all worlds. And it means you don’t need to settle on one particular media. However, you’ll need to spring for the cost of several reactors – to say nothing of the aquarium reactor media.

But if it’s a possibility for you – in terms of money, time, and space – you’re in the clear. You won’t hurt your aquarium.

Which Water Parameters Need Improving?

However, the bigger question that helps most aquarists settle on their aquarium reactor media relates to the health of their tank. Usually, you’re reaching for a reactor because of cloudy water or problems with water conditions. So the most practical consideration for deciding what aquarium reactor media to use is to look at the water parameters you need to improve the most:

Now, you CAN find other aquarium reactor media out there (calcium, Kalk, and Zeovit), but these three are the most popular and the easiest to handle. As such, they’re the three we’ll discuss. If you feel the need to progress to more challenging reactors, you can always move up down the r

Activated Carbon

Activated carbon is an old-school aquarium reactor media that’s been around since the dinosaurs.  (Okay, so dinosaurs didn’t keep aquariums – at least, that we know of. It’s the best way to describe how ancient this media happens it be) It’s one of the purifying agents inside your Brita® water filter. Activated carbon is famous for removing chemicals from water, which is why it shows up in plenty of filters.

Activated carbon filters out:

  • Chlorine
  • Heavy metals
  • Dissolved organics
  • Pesticides (hopefully you don’t have this in your water – aquarium OR drinking)
  • Tannins
  • Dyes
  • Phenols
  • Odors
  • Ozone

Two Little Fishies HydroCarbon Activated Carbon

Two things are essential with activated carbon as an aquarium reactor media: the particles’ size and shape. Round, regularly shaped, small particles pack better into a reactor, providing more surface area. That provides more filtration capacity and improves the efficiency that you need. Larger, irregularly-shaped particles offer less surface area as they pack less closely. This means you get less overall surface area and end up with a more limited filtration capacity.

Activated carbon is one of the most popular and inexpensive aquarium reactor media options out there.

The Link Between Activated Carbon and HLLE

Obviously, you can’t go wrong with popularity (or a break for your bank account). But I advise you proceed with caution when choosing activated carbon as your aquarium reactor media. A 2011 article demonstrated a link between carbon and head and lateral line erosion (HLLE). HLLE occurs where a stressed fish develops sores on the head and lateral line. According to the study, carbon dust particles were found embedded in the lateral lines of the fish suffering from HLLE.

If you plan to run activated carbon in your tank, take the time to read the article. If you skip it, my takeaway is that it’s absolutely essential for you to thoroughly wash the carbon aquarium reactor media to remove any dust particles. Don’t add the media to your water until you’re comfortable (and confident) it’s free of any fine particles.

Also, use an abundance of caution (i.e., avoid it) if you keep fish highly susceptible to HLLE – for instance, certain tangs.

Granulated Ferric Oxide (GFO)

Granulated ferric oxide (GFO) is an aquarium reactor media excellent at removing phosphates and silicates from aquarium water. Those are two water pollutants exceptionally “helpful” in growing problem algae. The name “granulated ferric oxide” sounds scary and like something we would try to remove from our tanks, but GFO has been used in aquariums to purify water for a long time.

GFO granules naturally have a high surface area – the prerequisite for any aquarium reactor media. And GFO acts as a magnet for phosphates, silicates, and other metals. When metals pass across the surface of GFO, courtesy of the the water current, ions get attracted to the ionic charge on the GFO. It isn’t precisely magnetism, but the concept’s similar. The metals “stick,” pulling them out of the water and removing the threat they pose to your fish and invertebrates.

Is GFO Sold Under Other Trade Names?

So you know how GFO works, and you may even want to add it to your aquarium reactor. But you’ve never seen “GFO” anywhere on a shelf. Why is that?

Granulated ferric oxide is the official name of the chemical in the aquarium reactor media. It’s a chemistry term any chemist or chemical manufacturer would recognize immediately. That makes it a commodity. But commodities don’t command premium prices in the aquarium market. Premium brands command premium prices. So GFO gets sold under popular trade names:

  • Phosban
  • PhosphateOut
  • RowaPhos
  • Phospure

Or you might have come across another option. Some phosphate-removing products are marketed under the chemical name granulated ferric hydroxide. The chemical compound is slightly different, but it works the same way as GFO.

On the other hand, Phosguard is NOT. Phosguard is a different compound altogether called aluminum oxide, It can also get used as aquarium reactor media, but it’s not going to remove your phosphates or silicates. So if that’s what’s troubling your aquarium, make sure you pick up the proper product.


The easiest way to describe biopellets is by going into the details of what they AREN’T. Activated carbon and GFO are aquarium reactor media that work via chemical reactions. Ions in the water respond to ions on the surface of the media, becoming chemically bound together and removed from the water column. In contrast, biopellets are aquarium reactor media feeding beneficial bacteria that actively CONSUME the pollutants in the water – no reaction required.

Dr. Tim's Aquatics NP-Active Pearls Aquarium Media Reactors

You still get that boost of surface area – courtesy of the round shape of the pellet – but you’re “juicing” your tank’s system. The food helps bacteria eliminate high levels of nitrates. It isn’t the media, precisely, doing the work. But without the help of the nutrients the biopellets provide, you’d still have a problem.

Solid Dosing vs. Vodka Dosing

When hobbyists turn to biopellets, you might hear them discuss a term called carbon dosing. Carbon dosing involves purposefully adding a dose of biologically available carbon to the water to act as food for the bacteria. Those microbes then remove pollutants like nitrates and phosphates from your water. And you have two options for carbon dosing: solid dosing or vodka dosing.

Solid dosing happens when biopellet aquarium reactor media goes into a reactor or even straight into a sump. The carbon (and other nutrients) in the pellet nourish those healthy bacteria. And your tank benefits from the increased growth.

Then you have vodka dosing. Yes, people actually add vodka (or another distilled spirit) to their tanks. It sounds strange (or questionable), but the response is the same – provided you’re doing things correctly. Of course, vodka dosing doesn’t offer additional nutrients the way biopellets do. So you need to weigh the pros and cons of using aquarium reactor media over that trip to the ABC store.

Aquarium Reactors for Aquarium Reactor Media

Once you’ve settled on your aquarium reactor media, it’s time to add it to your tank. You don’t want carbon or biopellets floating loose in your aquarium. So you need a way to confine the media where it’ll do the most good (and not look horribly unattractive). And one of the most efficient ways is to add an aquarium reactor to your system.

Two Little Fishies Filter Media Reactor

Aquarium reactors contain the media (and additional filtration sponges) to optimize the contact time between the water and the surface area of those reactor media. A pump or a manifold from your sump pushes the water through the main chamber. Then the water flows from the bottom, through the aquarium reactor media, and out to your tank. It’s the final stage of filtration, ensuring clean, CLEAR water.

You’ll find plenty of different styles and sizes for your reactors. And they usually work with any media type. It makes setting up this additional piece of equipment easy.

Going Low-Tech

Of course, you don’t HAVE to pick up a reactor. Suppose you want to test the benefits of using aquarium reactor media in your tank before committing to a reactor. In that case, you can simply buy the media and a media bag. Then all you need to do is put the media bag in an area of high flow within your sump.

Seachem Aquarium Reactor Media Bag

Going this route, your aquarium reactor media won’t work as efficiently as in a reactor because it ends up lying flat. But it WILL work, and any surface area within the media bag that gets exposed to a reasonable amount of flow will do its job properly. It’s enough to provide you with that test to see if the investment of the reactor is worth it.

Cautions for Aquarium Reactor Media

You need to take things slowly in this hobby under most circumstances. You can’t ignore or delay handling massive problems, but minor issues are generally best dealt with by deliberate, cautious improvements rather than dramatic changes.

The aquarium reactor media we have access to today are powerful, capable of significant improvements in water quality. And that sounds fantastic (because it is), but you need to consider how quickly you implement those improvements.

If you’ve had your tank running for five years a certain way, you don’t want to suddenly blast things with three oversized reactors overnight. You’ll shock the system (and all of the animals in it). I recommend starting small and increase the number or size of reactors over time.

The other thing you shouldn’t ignore is that link between activated carbon and HLLE. HLLE is a severe condition. You need to pay close attention to your fish when adding carbon, especially if you keep susceptible species. Discontinue the activated carbon as your aquarium reactor media if you see any worsening (and scale up your particle filtration capabilities in the meantime).

For More Information

When you’re considering adding any equipment to your tank, you want to do your homework. Not only because of the expense involved but also to make sure you have any questions answered. (Nothing worse than installing something and finding you don’t know how it works!) As aquarium reactor media adjust your water parameters, you want to have as much information as possible. And that’s where a few more chunks of info can’t hurt.

Let’s start with a quick YouTube video on aquarium reactor media and the reactors themselves:


And then you can move on to this YouTube video on setting up your own DIY biopellet reactor:


Activated carbon’s a popular aquarium reactor media. But you don’t want to risk HLLE. What are some of the fish you need to monitor?

Share Your Experiences with Aquarium Reactor Media

What has your experience with aquarium reactor media been? Any thoughts, advice, or real-world evidence to share? Let me know below!

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