Hi Mr. Goemans,
I'm a saltwater fish enthusiast, and have an idea that may work to reduce nitrates. It first involves building a chamber, which would be nothing more than a four foot section of 3" pvc that is filled with 2 -4 mm aragonite substrate and uses a 3" adapter on one end and on the other end, a 1 1/2" adapter. Then pump water into it through the 3" adapter and let it more slowly flow out the 1 ½" adapter, which would establish the presence of anaerobic bacteria, which in turn would reduce the nitrates! Is this something people are already doing or, would it really work? But to me, it sounds good in theory. What do you think?
Myrtle Beach, SC
This reduced flow through an enclosed chamber filled with some sort of substrate for bacterium adhesion is a form of denitrification, which has been used in one form or another for decades, both with and without certain additives to enhance its microbial colonies. In fact, the gravel is not needed if you simply run the water with the dissolved nitrate through a 'very' long piece of airline tubing, as its oxygen/nitrate content will be used up by the time it exits the other end. In fact, such a device was widely sold in the trade many years ago, however, has fallen out of favor with aquarists as it was usually quite unreliable.
The problem with all these type ideas/equipment has been correctly controlling the water flow through its internal areas. Too fast a flow does nothing; too slow a flow results in hydrogen sulfide and/or nitrite. And keep in mind there are two classes of anaerobic bacteria, therefore the oxygen content of the water flowing through the device is critical as to what results it will render. To better understand these processes, visit my website and open the Guest Articles page and read the 'Sandbeds Part I & II' articles.
In closing, its not impossible to come away with some good results with a somewhat similar device (different dimensions), however, the time needed to precisely control the flow through it and the water testing associated with it, could easily become an enormous time consumer. And of course, it would be risky to allow the effluent from the device to reenter the aquarium until its safe. Furthermore, once up and running correctly doesn't mean it will continue that way, and frequent effluent testing is a must, and by frequent I mean every couple of days as the processes can swing from adequate to dangerous very quickly!.
Hope this helps,