CerMedia Marinepure Block High Performance Biofilter Media (8X8X4 In)

CerMedia MarinePure’s ceramic bio-filter media combines vast surface area with open-flow porosity for ammonia and nitrite removal in marine and freshwater tanks.

Ceramic Bio-Filter Media with Vast Surface Area AND Open-Flow Porosity. Designed to improve upon deep sand beds or live rock to lower nitrates in marine freshwater aquariums. Will also remove ammonia nitrites. Use in sumps or in extra large filters.

• High Performance Biofilter Media
• Suitable For Fresh And Salk Water
• Provides Consistent Water Chemistry

See our guide to Live Rock for how it fits into a reef tank's biological filtration and aquascape.

The CerMedia Marinepure Block High Performance Biofilter Media (8X8X4 In) is a biological media, giving nitrifying bacteria surface area to colonize — see our guide to choosing filter media for how it fits alongside mechanical and chemical stages.

Specifications

Dimensions: 8 × 8 × 4 inches — about 203 × 203 × 102 mm
Form: one solid block
Designed for: ammonia, nitrite and nitrate removal
Primary role: deep anaerobic zones for denitrification in passive or low-flow systems; a live rock substitute
Where it goes: aquarium sumps, or in the display as part of the scape
Water types: fresh and salt
Service life: designed to last indefinitely; CerMedia say the block will last many years

Material: inert aluminosilicate ceramic, fired above 1000 °C. CerMedia state it will not leach anything into tank or pond water, and that it is stable in both fresh and salt water.

Capacity — CerMedia's own rates, and they are two different numbers:

For ammonia and nitrite (nitrification), one block per 500 gallons — about 1,900 litres.
For nitrate (denitrification), one block per 150 gallons — about 570 litres.

The gap between those two figures is the most useful thing on this page. If you are buying the block to handle your bio-load, one block covers an enormous tank. If you are buying it to bring nitrate down, you need more than three times as much of it. Work out which job you are buying it for before you decide how many to order.

It is brittle, deliberately. CerMedia explain that the walls of the large pores have pores, and those pore walls have smaller pores again — which is how you get high surface area and open porosity at the same time, and why the fine structure is weak. Handle it as little as possible.

Easy to shape. The block can be cut with a hand saw or worked with coarse sandpaper, which is what makes it usable as an aquascaping rock rather than only as a sump component. Rinse the particulate off before it goes back in the water, and wear a dust mask while you cut.

What CerMedia do not publish: a surface-area figure in square feet or square metres for the Block, and no weight. Figures circulate online; none of them come from CerMedia and we are not going to repeat them. The capacity rates above are the manufacturer's own and are the numbers to buy on.

Setup & Use

Rinse it before it goes in. CerMedia's first instruction, every time: rinse to remove the surface particulate created in shipping. If you rinse in tap water, rinse again in tank water to get the chlorine off. Wear a dust mask if you are handling it dry or cutting it — this is a fired ceramic and the dust is not something to breathe.

Put mechanical filtration ahead of it. CerMedia recommend filter matting or equivalent before the water reaches the media. The open pores are the whole product; feeding them raw detritus is how you lose them.

It does not cause a mini-cycle. The media is inert and sterile, so adding it does not disturb an established tank — it simply gives the bacteria you already have somewhere better to live. It also holds water, so if the flow stops or you lift it out of the filter, the colony stays alive far longer than it would on a plastic bio-ball.

For ammonia and nitrite: put the block where the water flows. In a filter, a sump, under a gravel bed, or in the tank itself — CerMedia are relaxed about where, and specific that locating it in the flow gives the most efficient result.

For nitrate, do the opposite: put it somewhere passive. CerMedia's instruction for denitrification is a low-flow or still location — a quiet corner of the sump, under a gravel bed, or built into the reef structure. The reason is physical: the block is thick enough that the oxygen in the water passing through it is used up before that water reaches the middle, and the low-oxygen core is where denitrifying bacteria live. Park it under a return pump and you have destroyed the anoxic core and bought an expensive ammonia sponge.

Nitrate removal also needs a carbon source, and CerMedia say so. Denitrifying bacteria need carbon as well as low oxygen. If you are not already dosing a carbon source, the block alone may not move your nitrate much — and CerMedia are honest that bacterial nitrate removal is very system-dependent.

As a live rock substitute. CerMedia position the block against live rock directly: more open porosity, contaminate-free, no hitchhikers, no die-off, lighter, and it can be sanitised and reused. It can be shaped to look natural and hidden behind a false wall or under gravel. It is also, they note, a good home for copepods.

Maintenance: almost none. CerMedia's advice for a block in a passive location is to rinse it once when it arrives and then leave it alone — because it is brittle, and because handling it is the main thing that damages it. In a flow-through filter, a backwash or a rinse in tank water every three months, or as often as your system needs. If it ever needs more than that, a weak acid can be used, but keep the time in acid short and wear proper protection.

Give it time. CerMedia are blunt that the media does not do the work — the bacteria do, and bacteria need time to grow and multiply. A new block is not a new filter on day one.

Freshness & Storage

Every batch we dispatch carries a minimum of 6 months' remaining shelf life. Store this product in a cool, dry place away from direct sunlight, with the cap or inner foil closed tightly after each use.

Filter media and substrates carry no manufacturing or expiry date — their working life begins on first contact with water, not on the shelf.

Returns & Replacement

Returns are accepted within 7 days of delivery, provided the item is unused and in its original packaging. Manufacturer-sealed items cannot be returned once the seal is broken, and sale-priced items are not refundable.

If your item arrives defective or damaged, message us on WhatsApp with your order number — or email us, if you would rather — and we will replace it. Approved replacements are delivered within 3 to 5 business days. Transit damage is covered by insurance on every shipment. If tracking shows delivered but nothing reached you, tell us within 72 hours, which is the reporting window Indian couriers allow. Damage caused during installation or use is not covered; replacement spares for such cases are chargeable.

Full terms are on our Cancellation & Returns page.