Seachem Laboratories Denitrate is a natural biological filter media that works in the same way as live rock in saltwater aquariums.

Made of a natural mineral, the microscopic pores on each grain of Denitrate becomes home to colonies of anaerobic bacteria that convert nitrate to harmless nitrogen gas.

Denitrate Flow Rates

If using Denitrate in a canister filter or power filter, it is recommended that flow rates do not exceed 50 gallons per hour. Higher flow rates will introduce too much oxygen into the Denitrate media, reducing the populations of anaerobic bacteria and promoting aerobic bacteria. As we learned on our page on the Nitrogen Cycle, aerobic bacteria convert nitrite to nitrate while anaerobic bacteria convert nitrate to nitrogen gas.

Too much aerobic bacteria and Denitrate will become a ‘nitrate factory’, with not enough anaerobic bacteria to convert nitrate to nitrogen gas!

For higher flow applications, it is recommended that Matrix or Pond Matrix products be used instead of Denitrate. Matrix is similar in material to Denitrate, only larger, thus allowing for deeper anaerobic zones that are not as affected by higher flow rates.

seachem matrix

Instead of Denitrate, Matrix is used in high flow areas

Denitrate Placement

As mentioned, Denitrate can be placed in a canister filter, and since some hobbyists will use Denitrate in this way, it bears mentioning. Personally, I feel that canister filters have no place in a saltwater aquarium setup!

In a saltwater aquarium setup, Denitrate should be put in media bags which can then be placed in the aquarium sump. My preference is to lay the bags in the second compartment of my aquarium sump, after the protein skimmer. Filter floss placed before the second compartment can also help to trap any detritus before it reaches the Denitrate media, but is not really essential.

If a sump is not available, Denitrate can be also be used in the media compartment of a hang-on back power filter.

In sumpless systems, Denitrate in media bags can be placed in a discreet corner of the tank where they can be accessed and removed for routine cleaning.

Denitrate can also be used in a media reactor such as Phosban’s Phosphate Reactor, but I find this to be more trouble than its worth, since it already works so well just placed in the aquarium sump.

However you wish to use it, always ensure that Denitrate is placed below water. Using it in a drip-tray or ‘wet-dry’ filter where is is exposed to air will cause Denitrate to function as an aerobic filter.

Cleaning Denitrate

In order that the pores of Denitrate do get too clogged with mulm and detritus, it is advisable to rinse the media bag with Denitrate lightly in aquarium water with each water change. Aquarium water that has been siphoned out and is destined for the drain is ideal for this purpose.

Place the bag of Denitrate in aquarium water and simply ‘massage’ out most of the mulm and detritus. Once the water turns brown and cloudy, stop and return it to the aquarium sump. Don’t rinse more than is needed as this will destroy your bacteria population!

It is important to note that Denitrate, or any other biological filter media should be rinsed in aquarium water only. Rinsing it in tapwater or freshwater will immeditely kill the beneficial marine bacteria that we have taken so many weeks to cultivate.

Having two or more media bags filled with Denitrate means that we will be able to rinse each bag in turn with every water change, minimizing the impact on our aquarium’s biological filter.

How Much Denitrate To Use?

500 mL of Denitrate treats about 50 gallons of water. Since it is impossible to overdose Denitrate, I prefer to use about twice the recommended the amount, placed in several large media bags.

If your nitrate levels are already very high, say 100 ppm, it will take Denitrate quite a few months to bring it down to about 50 ppm.

If your nitrates are that high to begin with, it is best to trace the root of the problem (overfeeding aquarium fish and overstocking are the most common reasons) and tackle that as well.

It will take several weeks for the populations of anaerobic bacteria to reach levels where they can effectively reduce nitrates. In the interim, a series of regular water changes are advised, to bring down nitrates to manageable levels of say, 25ppm.

With long term use, Denitrate is a highly effective complement to any marine aquarium’s biological filter.

More On Saltwater Aquarium Filtration:

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