Thoughts on the DIY Coil Denitrator

Of all the articles that I've contributed, none has received the attention nor generated the kind of response as has the Coil Denitrator project.

As such, I thought it about time to offer some follow-up and additional information on the unit. Since the original article pretty well described what the "C-D" does, I won't repeat that now. However, I will continue the story by saying that once installed, adjusted and allowed to fully cycle, immediate results are NOT going to be seen.

Most of the feedback I'm getting is stating that the effluent isn't giving a "0" nitrate reading on test kits. It won't. The theory, (incorrect) that nitrate-enriched water goes in and pristine water comes out is an oversimplification. Nature isn't quite so straightforward. The process of developing the anaerobic bacteria colonies is a slow one. All of the water in the C-D is oxygen rich, (at least as far as this subject is concerned) during the first several weeks. Essentially, all we have is an additional nitrification filter. The unit is actually going to PRODUCE nitrate just like your main biological filtration bed for awhile, so don't be concerned that you've done something wrong!

Far from it...things are progressing just as they should. Once the coiled tubing becomes populated with bacteria, the purpose of all those coils begins to pay off. Actual denitrification does NOT take place in the coiling...it occurs in the oxygen-starved center chamber where we placed all those bioballs. By retarding the outflow using a valve, we are allowing the water to "stagnate" to the point that dwell time is elongated, thereby allowing the anaerobic bacteria to commence eating and converting whatever nitrates are present. This is a good time to point out that bacteria colonies grow and recede depending upon food availability. The more nitrate present, the larger the colonies become to handle it. As nitrate levels decrease, so too, do the bacterias. This is truly a dynamic filtration concept that allows for Nature to do her thing. The coiling slowly strips the water of oxygen as it makes it's way down and around the inside of the cylinder. The hearty aerobics populating the upper third of coils eventually gives way to their anaerobic cousins at the bottom. How? Aerobics consume oxygen during the conversion process of ammonias into nitrites and nitrates. Anaerobic bacterias require NO oxygen in order to convert nitrate into nitrogen gases. All we are doing is providing a dark, stagnate environment for these bacterias to flourish. Essentially, a hands-off operation.

Think of it this way, when you connect a chiller to your water system, the overall temperature of your tank doesn't immediately drop. It takes days for the continual cycling of water through the chiller to "pull-down" the ambient temperature to your target range. When you add a kalkreactor to maintain dKH, the effluent actually has a very low pH reading, sometimes really acidic. However, over time the system stabilizes and pH along with dKH return to the desired levels. The CD is no different. It's going to take time to see any results from your project. This is a long-term maintenance device.

Depending on the physical size you constructed, the efficiency of the bio material you chose to install and the volume of water you expect to be processed, the coil denitrator is going to perform accordingly. If you start with a very heavy concentration of nitrates in your water, the time the CD takes to actively start the conversion process will be shorter than if you place the unit on a new system with a fresh salt mix. Even then the process is a slow one.

Ideally, the CD should be checked periodically to insure the drip rate is ok...other than that it should be ignored and allowed to quietly develop it own processes.

If your need is immediate removal of damaging nitrate, then I suggest water changes. The coil denitrator is a long-term solution to an ever-present and on-going condition whenever livestock are present.

There's no science in this article. No references, bibliographies or the like; nothing to base my comments upon other than my own personal observations and experiences.

I can tell you though that I maintained a well stocked reef system with some fish for many years using nothing but a skimmer and a CD for nitrate control. It did exactly what it was supposed to do and allowed me more time to actually enjoy the hobby and not to fret over it.

Don Carner

Toledo, OH