DIY Coil Denitrator

4. The Ball Valve, (or drip-rate adjuster).

Here’s the heart of the entire project! As important as the choice of bio media is, the quality and accuracy of the valve that controls your drip rate will make or break this project!

Many, many folks have commented on restricting the output on their pumps. Somewhere, someone once mumbled that restricting a pump in any way would ruin it. URBAN MYTH! While it IS true that you should never, EVER restrict the INTAKE of any pump, there is absolutely NO harm done to any pump when you throttle it at the OUTPUT side! The impellor will continue to spin at it’s rated volume without any detrimental impact.

Having said that, let’s look at how this should work.

The pump, (powerhead) draws the tank water and “pushes” it into the denitrator cylinder. You can feed the pump from a sump or by placing it directly into your aquarium if you aren’t running a sump-system. Either way works but if you feed from the aquarium itself, make sure to use a pre-filter over the intake line! Actually, this isn’t a bad idea for a sump-feed setup either…this will prolong the inevitable buildup of detritus inside the denitrator and assist in keeping everything as clean as possible.

Attach your choice of ball valve or similar to the OUTPUT side of the denitrator.
Remember that you installed 2 fittings during the construction phase. Depending upon your selection of product, you MAY have to use the same method of reducing the tubing diameters as you did when tapping off the pump. I chose the Kent Marine Reverse Osmosis ball valves as they are the correct size and are also small enough to fit in the limited space under a cabinet/stand. By starting with a wide-open flow rate, slowly begin to close the valve until a steady dripping is evident at the output side of the valve. Run your hose back into the sump or into the aquarium and secure it so it doesn’t flop out onto your carpet and ruin your whole day!

Your target drip-rate is fast but not a steady stream! You’ll have to experiment a bit depending upon the model and operation of the valve. Essentially, that’s it!

Ok, now the boring part…the theory behind the design and why you do not have to feed this unit like some other designs on the market.

The concept of this project is a hands-free, fiddle-proof addition to your existing system of reef or fish-keeping endeavors. Results are not instantaneous!
A normal 6 to 7 week cycling is required for the necessary anerobic bacterias to establish themselves AND for the aerobic bacterias to colonize the inside of all those coils winding their way down the inside of the cylinder. Both types of bacteria are required to work in harmony with this unit. Here’s a quick overview of how the whole thing works:

As tank water is pumped into the reactor, it is laden with all the chemicals inherent within the system including nitrates. Also present is oxygen,(referred to as O-2). Anerobic bacteria cannot survive with even the smallest traces of O-2 and to eliminate this gas from our reactor we have provided all that surface area within the coils for these O-2 munching helpers. As the water works is way down and around the coils, the aerobics strip the water of all O-2 as they convert ammonias into nitrites. The nitrites then enter the center chamber and flow back out into the aquarium. This is why you will test positive for trace nitrites when checking the effluent going back into your tank. In fact, you may experience a higher concentration of nitrites than you have since 1st cycling your system way back when. Don’t be alarmed…this condition is perfectly normal and part of the cycling process of your denitrator.

Slowly, as more and more aerobics inhabit the coils the amounts of available O-2 in the lower portions of the coils will become smaller and smaller. Eventually, all the bacteria in the upper reaches will have depleted the O-2 by the time the water enters the center chamber. Now is when things begin to happen!

O-2 depleted water  now occupies the center section of your chamber. The bio media provides the area for the denitrifying bacteria to gain a foothold and begin to florish. The amount of nitrate concentrations will ultimately determine the size of this colony once fully established. Naturally, the colony will expand and contract as the available nitrates fluctuate. Relevant to this project is patience!

You aren’t going to see results for almost 2 full months so sit back and monitor only the drip rates as your denitrator matures.

I’d like to mention “feeding” at this point. There isn’t any. Period. Resist the urge to add lactose, milk sugar or any other type of “food” to this system! Doing so will NOT improve, increase or otherwise speed up the process of O-2 depletion or the creation of your anerobic bacteria! Actually, adding these may only serve to clog up the available surface area of the bio materials within the cylinder. Remember too, that these foods could ultimately pass through the denitrator and enter your main display system, having an adverse impact on delicate corals, inverts or fish. The whole point here is to NOT add anything but to allow Nature to develop and mature the process without human intervention.

The amusing thing about using this method is that the coils have nothing to do with the actual conversion of nitrate into nitrogen. All they do is to provide surface area for aerobic bacteria to strip the water of all available oxygen as it works it’s way into the center section. The name, “Coil Denitrator” is a misnomer in that it should be called a Tower Denitrator due to the “action” taking place on the surface area of the bio materials inserted within the coils during construction.
I think that this is where a lot of the confusion over the project enters the picture.
The slow flow rates allow the water to “stagnate” to the degree that dwell time is provided for the conversion process. Too fast a flow and complete breakdown cannot occur, resulting in nitrite production. Too slow a flow rate and the possibility that hydrogen sulfides might be produced. You’ll know when this happens as the odor of the water leaving the reactor will smell like rotten eggs.
This is a bad thing and the effluent should NOT be allowed to re-enter the main water system! Simply increase the flow/drip rate and discard the effluent until the odor diminishes. Top off your sump/aquarium accordingly with fresh water to compensate for this loss in water volume.

Once matured and fully established this project will assist in your nitrate control and allow you to better enjoy the hobby rather than sweating over it.

I hope that I have cleared up any misconceptions and better explained the construction process this time out. Remember to use a good prefilter prior to your pump to insure years of clog-free operation. If you are using a sump, simply place your intake line behind a water dam to trap detritus and mulm before it enters the intake hose. For those of you without a sump and that have to place the pump/powerhead directly within the aquarium, use a commercial prefilter similar to Hagen’s  that connects directly onto the intake side.

Thanks for your interest and the best of luck with your project!

Back to the beginning.

Click on each of the DIY Coil Denitrator components below to see the enlarged views and pertinent information.

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