DIY Coil Denitrator Plans

  • 01 of 10

    DIY Coil Denitrator Plans: How It Works

    DIY Coil Denitrator Plans - How it Works
    Don Carner

    Here's how the Coil Denitrator 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 O2). Anaerobic bacteria cannot survive with even the smallest traces of O2 and to eliminate this gas from our reactor we have provided all that surface area within the coils for these O2 munching helpers. As the water works its way down and around the coils, the aerobics strip the water of all O2 as they convert ammonia 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. You may experience a higher concentration of nitrites than you have since first 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 O2 in the lower portions of the coils will become smaller and smaller. Eventually, all the bacteria in the upper reaches will have depleted the O2 by the time the water enters the center chamber.

    O2 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 flourish. The amount of nitrate concentrations will ultimately determine the size of this colony once fully established. The colony will expand and contract as the available nitrates fluctuate. 

    The diagrams, along with this article illustrate the main cylinder, the ball valve, and pump assemblies. In reality, these are all the components needed to establish a nitrate-removal system on any saltwater application. So, let’s begin:

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  • 02 of 10

    Denitrator Cylinder

    Denitrator Cylinder
    Don Carner

    For systems up to 125-gallon capacity, a cylinder 18 inches by 3 inches will provide adequate volume to establish the necessary bacteria colonies for moderate bio-loads. Moving up to a 24-inch height will provide that “extra margin” if your animal population is on the “heavy” side. For those of you with fish-only systems, you may wish to enlarge the diameter to four inches to allow for more bio-media.

    Start by thoroughly cleaning the PVC of all oils and residues after cutting to length. Ensure that all “flash” is removed from the ends by lightly sanding the cuts and slightly rounding the edges. This will ensure a water-tight glue joint later.

    Choose your top and bottom caps. We used standard PVC lead out caps, utilizing the flanged style for the bottom, (this also serves as additional support). Purple dope the inside of the bottom cap and the bottom 1/2 inch of the cylinder (on the outside only). Apply the PVC cement over the dried purple dope and attach the bottom to the cylinder. Careful because it is an almost instant bond. Now on to the fun part.

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  • 03 of 10

    Denitrator Cap, Base & Fittings

    Denitrator Cap, Base & Fittings
    Don Carner

    The lid or "cap" should be drilled to accommodate the two fittings, intake, and output. No other modifications are necessary. A secure, watertight fit is essential between the fittings.

    The bottom or base of the unit is sealed permanently to the cylinder. Diameters will vary depending on the size you decide to construct.

    There are two fittings needed. Red indicates the input side. Here, you attach the tubing to be coiled down the inside diameter of your cylinder. Match the fittings to the size of the tubing you select. We prefer 3/8. I.D. now over 1/4 inch. Blue represents the output fittings. Nothing is attached here, allowing the internal water pressure to force the processed water back into your sump or display tank. There are no moving parts, nothing complicated nor any special knowledge needed other than the tools and materials needed for assembly.

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  • 04 of 10

    Making Coiled Tubing

    Making Coiled Tubing
    Don Carner

    Use the same diameter pipe or PVC cylinder as you plan on using for your denitrator. Take your length of tubing, (NOT thin-walled vinyl!) and hand coil it so that it will fit inside a large dutch oven or similar pot. Fill it with water and bring it to a raging boil. While boiling, carefully place your hand-coiled tubing into the pot.

    Depending on the thickness of the tubing wall, the time necessary to get the tubing "pliable" will vary. Experiment a bit. Once you have the tubing soft, remove it from the water and commence wrapping it around your cylinder. Work quickly as your tubing will cool very fast! Use duct tape or similar to hold your coils in place. You may have to use several "segments" before you get the entire length completed. These lengths can be connected with vinyl hose later. Keep the coils tight together, and as they cool, they should retain their new shape.

    Remove the coil from the cylinder form and insert the coil inside the cylinder. Run a piece of tape down the inside of the coils. Remove the taped coil from the cylinder. You can now daub silicone in between the coils. You don't need to do any tape and glue things. If you have already attached the bottom to your cylinder, just work the coils into the unit and continue your final assembly.

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  • 05 of 10

    Using Pre-Coiled Tubing

    Using Pre-Coiled Tubing
    Don Carner

    We use pre-coiled airline tubing from Walmart. Fifty feet is around $7.00 and is found in their hardware department. The bright yellow color is inert and will not impact your livestock. Also, the inside diameter is perfect for this project! 1/4 inch ID is ideal but you can go up to a 3/8 inch ID if you prefer. Remember, the unit is sealed and cannot be cleaned once finished!

    Please note that you’ll have to cut the brass air pressure fittings off both ends of the coils before dropping into the PVC cylinder. The bottom cut-end of the coils simply rests at the bottom of the cylinder, unattached to anything. The top cut-end of the coils will be attached later to the nipple fitting attached to the lid.


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  • 06 of 10

    Install the Biomedia

    Now we insert the bio-media down inside the coils that have been installed into the cylinder. This is probably the most important decision-making in the entire project. The quality of the media and the available surface area will determine the ultimate success of your denitrator. After all, it will be the ability of the bacteria colonies to expand and contract as the food source increases and decreases, which will ultimately contribute to those lower nitrate concentrations.

    We used BioKaskades (small) in my prototype reactor but any good spiked ball or BioPak will do. Avoid DLS or other mat-type materials as ​these clogs and hold detritus much too easily. We would also caution against any sintered glass media. These have a phenomenal surface area but again, are so closed-cell that clogging could be an issue over time.

    Once the inner area has been loaded with your choice of media, it is time to attach the top, cut-off end of the coiled tubing to the intake nipple.

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  • 07 of 10

    Denitrator Cap, Base & Fittings

    Denitrator Cap, Base & Fittings
    Don Carner

    Drill two holes into the top lid before attaching to the main cylinder body. Install two nipples or fittings that will accommodate the size of tubing used inside the cylinder. Nylon or vinyl fittings must be used.

    Remember that the unit will be slightly pressurized once completed and running. Ensure all glue joints and fittings are secure and water-tight. We used pipe tape on the threads of my two fittings and torqued them into the lid before sealing with epoxy cement.

    Once cured, purple dope the inside of the lid lip and the top 1/2 inch outside of the cylinder. Once dry, apply PVC cement as you did to the bottom cap and install the lid to the tube. Your denitrator is complete.

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  • 08 of 10

    The Drive Pump (or Powerhead)

    Denitrator Pump
    Don Carner

    Although you can use a siphon method to supply your system water to the denitrator, We chose to power drive our project. Siphon feeds are unreliable in our experience, (restarting a broken siphon has never been one of our favorite things).

    As such, you’ll need to match the pump’s output tubing to the denitrator’s smaller intake fitting. The diagram shows the “step-down” method used to accomplish this. Start with a piece of tubing that will fit over your pump’s output nozzle.

    Next, insert the next size smaller diameter tubing into that, repeating the process until you have achieved a good fit at both ends of the line, at the pump output and the denitrator’s input. Secure each connection with a nylon tie-wrap or stainless-steel hose clamp.

    We always drop the short lengths of tubing into boiling water first to soften them up. This makes inserting them so much easier. Once done, run cold water back over the assembly and this will “tighten” them all up. You are done.

    There is no adjustment to the pump's output velocity at this time. The pump will operate at it’s rated output velocity in this installation.

    Now we get to 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. This is an urban myth. While it is true that you should never, ever restrict the intake of any pump, there is 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.

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  • 09 of 10

    Denitrator Ball Valve

    Denitrator Ball Valve
    Don Carner

    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. 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 a ball valve or similar to the output side of the denitrator. Remember that you installed two 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. We 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 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.

    The concept of this project is a hands-free, fiddle-proof addition to your existing system of reef or fishkeeping endeavors. Results are not instantaneous! A six- to seven-week cycling is required for the anaerobic 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.

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  • 10 of 10

    How It Works

    How It Works
    Don Carner

    Slowly, as more and more aerobics inhabit the coils the amounts of available O2 in the lower portions of the coils will become smaller and smaller. Eventually, all the bacteria in the upper reaches will have depleted the O2 by the time the water enters the center chamber. Now is when things begin to happen.

    Oxygen-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 flourish. The amount of nitrate concentrations will ultimately determine the size of this colony once fully established. You aren’t going to see results for almost two full months so sit back and monitor only the drip rates as your denitrator matures.

    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.

    We 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.

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