What Is a Coil Denitrator, and How Does It Work?

A Nitrate Reduction Method for Saltwater Systems Explained

Coil Denitrator Graphic
Coil Denitrator Graphic. by Don Carner

Nitrate isn't good for any saltwater system, be it an FO (fish-only), FOWLR (fish-only w/live rock), or a reef aquarium. To accomplish nitrate reduction and eliminate the levels of nitrate that build-up in closed saltwater systems, you can buy a commercial denitrator unit that costs big bucks, is difficult to adjust, and requires feeding and monitoring to maintain proper operation. However, there is an alternative low-tech solution to very common nitrate woes. A simple coil denitrator!

What Is a Coil Denitrator?

Essentially nothing more than a cylinder with a coil of tubing and some bio-balls, this device works, and achieves the same denitrification results as the more complex and costly commercial units, but much more easily, as well as naturally.

How Does a Coil Denitrator Work?

A coil denitrator takes 5 to 6 weeks to cycle (yes, they cycle just like the tank). The quantity of product that is processed, (nitrate) is truly amazing, considering how once established there isn't anything more to do! So how does this happen? As oxygen-rich water is pumped into (G) and enters the top of the unit, (A) it is forced to spiral down through the layers of plastic coil tubing (E) until exiting within the center of the cylinder (C). As the water level increases within the body of the unit, the bio balls (F) become host to the millions of colonies of bacteria that commence multiplying. As the water reaches back up to the top, it exits through the other fitting (B), the one not internally connected that runs back to your sump or display tank. So? So, as the water slowly works it's way down the spiral, the O-2 is consumed by the AEROBIC (living only in the presence of oxygen) bacteria, the same ones that are in your filter and make all the life possible. Somewhere around 3/4th's of the way down, however, the O-2 levels diminish within the spiral, having been consumed by the aerobic bacteria higher up the coil.


Now what? Well, now the ANAEROBIC (can live in the absence of atmospheric oxygen) bacteria begin to flourish, the very ones that feed on nitrate, not O-2! As the water continues its travels it encounters the main interior chamber of the cylinder. All those bio balls are just waiting to provide an area for more anaerobic bacteria to consume all the nitrate that wasn't converted inside the bottom 1/4 of the coil. This is the "bank" that will allow the coil denitrator to continuously process more and more nitrate as it is produced within the display tank.

By the way, if you are using a wet-dry or trickle filter with ANY other media, you have a nitrate "producing" filter! Yup, that's what they are designed to do, convert ammonia ultimately into nitrates! Nothing like adding more in so we can spend more money to get it out, huh?