The Salty Side: Saltwater Aquariums for Beginners

Bio Media

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What is bio media?

Biological media, or bio media for short, refers to media used in a saltwater aquarium which encourages the proliferation of nitrifying and de-nitrifying bacteria, in addition to or as a direct replacement of live rock.

bio pellets
Aquamaxx Bio Pellets

How does it work?

The inclusion of live rock as your primary filtration is central to the success of your tank.  However, as is quite often the case, the capabilities of the nitrifying bacteria living among the live rock can become overstretched.  

Consider your tank a breeding ground for ammonia/nitrite loving organisms which expel nitrate as an end result.  Ammonia (in trace amounts) is introduced into your tank by the addition of fish and food, it gets quickly broken down into trace amounts of nitrites, and then into nitrate. 

To a certain extent, live rock can handle nitrate, converting it into nitrogen which is then expelled at the water surface.  However, adding more fish introduces more ammonia/nitrite/nitrate.

At a certain point the nitrifying bacteria living in your live rock will become inundated by the bioload imposed on them.  Unable to cope, nitrate will begin to steadily rise.  This is where additional biological media comes into play.

Bio media provides additional ‘living quarters’ to further increase the population of nitrifying bacteria in your tank, thereby tackling the additional bioload your live rock bacteria is unable to handle alone.

Types of bio filter media

There are a few different types of biological filter media on the market nowadays, all of which essentially do the same thing.  

For use in bio-reactors:

Media such as Aquamaxx biopellets and biopearls are made to be used specifically in a bio reactor.   

The pearls/pellets are placed in a purpose made Bio Reactor such as the Aquamaxx Biomaxx Pellet Reactor (not just any old reactor) and vigorously tumbled.  The environment created by the Bio Pearls becomes an ideal spot for bacteria to breed and proliferate.

As the pearls become active, which can take up to 6 weeks, they start to release a mulm.  This mulm is the result of nutrients being broken down in the reactor and needs to be effectively skimmed away to prevent the majority of it returning to the system.

For this reason you also need a very effective skimmer to ensure the mulm is removed with the reactor outlet being close to the skimmer intake.  Small amounts will find its way back into the system, but this is of no concern, and in fact, acts as a food source for corals.  

The level of the bio pearls should be monitored and topped up should they drop, but this typically only happens once or twice a year.

bio reactor
Aquamaxx Bio Reactor

Standalone bio media:

Bio blocks, bricks, plates, and spheres such as those made by MarinePure, have been developed to use both freshwater and saltwater aquariums.  They have proven to be especially effective in saltwater tanks. They are usually placed in the sump closer to the return than the inlet. This helps to keep them from becoming clogged with detritus.

Sera Siporax is another well known product, and is also used when you have available space in your sump. Although it may look a lot like other cheaper ceramic filter rings, it is different because it consists of sintered glass. This sintered glass has a three dimensional pore structure which is fine enough to offer the ideal conditions for nitrifying bacteria, and is self cleansing due to the interconnected system they provide. These come loose and are most often kept in media baskets, cups or bags.

Much like live rock, nitrifying bacteria will take residence on the oxygen-rich outer layers, breaking ammonia and nitrite down into nitrate.  In the inner oxygen-poor centre, denitrifying bacteria break nitrate down further releasing nitrogen gas.  

If you are limited on space, MarinePure Bio filter media would be the ideal solution.  These blocks can easily be trimmed down and shaped to fit any sized compartment.

Best bio media

There is one form of media that appears to be a forerunner when it comes to which bio media is best.  And that accolade goes to Marine Pure.  Marine Pure’s plates and blocks have been recommended by many a saltwater aquarium owners who have noticed a marked decrease in nitrates.  

The blocks and plates have other benefits, one of which is that they are extremely easy to slot into small spaces and can even be trimmed or shaped to suit.  They are porous and provide a large amount of surface area for nitrifying bacteria.  Despite their thickness, water is able to freely flow through the blocks and plates. 


How to use bio media?

Bio media is placed in the sump of your saltwater aquarium.  Smaller media such as pearls and pellets are placed in purpose made bio reactors.  

Medium sized media such as spheres, gems, rings etc. are placed in media baskets, cups or bags to keep them in place.  

Larger media such as plates and blocks are placed in the sump.  These can be cut to fit the size of the compartment you wish to place it in.  

How long does bio filter media last?

In the case of MarinePure, the manufacturer states that it can last indefinitely, much like your live rock would. Sera Siporax is another product that can last indefinitely.

When considering media that you would use in a bio reactor, these pellets continually tumble and are slowly reduced over time. It comes down to the system in which they are running. In a system with higher levels of nutrients biopellets are more prone to being utilised quicker.

When should I use bio media?

If your intention is to keep many fish, this will increase the overall bioload in your tank. Consequently a significant level of nitrate will need to be controlled and bio media may well be an advantage.

However, if you plan on keeping a system low on bioload, such as an SPS dominant tank, your live rock may be sufficient.  Every tank is different and it ultimately comes down to trial and error.

In my own experience, keeping an ultra low nutrient system ie. low levels of nitrates and phosphates, I had been using a refugium as my main nitrate export.

I decided to try Arcadia BioPearls in a Bio Reactor. Due to my very low nitrate level (below 1ppm), the biopearls never really became ‘active’.  Nitrate began rising so the Bio Reactor was removed and the refugium reinstalled.

I would suggest that bio media only becomes significantly effective when nitrate levels exceed 5ppm or more.

What does 'seeding' mean?

This simply means that you are allowing nitrifying bacteria within an established saltwater (or freshwater) aquarium to populate whatever filter media you are placing in your tank.   As you can see below, there are a few different types of media available but they all essentially do the same thing. 

How long does bio media take to seed?

In an established tank, it takes roughly 2 weeks to seed. 

In a new setup, like live rock, bio media will take a minimum of 6 weeks to cure (or seed). 


This is useful to know when setting up a quarantine tank. QT tanks are normally run on seeded filter sponges and can be just as easily run with bio media.  If you’re setting up a quarantine tank, which I highly recommend when adding new fish and invertebrates to your display tank. 

It is worth mentioning here that should you need to set up a hospital tank and you will be using a copper treatment, then seeded sponges and bio media should not be used.

You may find this article on quarantining helpful. 

So there you have it!

Any of the above manufactured products will take some time to become live, as live rock itself does.  This process(we could call it curing) should take approx. 6 weeks before you start to see any benefit in it.

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