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Instructions for building a simple coil or flat panel denitrator

                      D E N I T R A T O R    P L A N S

Instructions on how to build your own low cost Denitrator!

Please excuse the simplicity of the explanation of this concept.

Part 1 - Basic considerations for Denitrification of Salene Waters:

In order for denitrification to occur, all oxygen must be consumed from the water and facultatively aerobic/anaerobic bacteria must form. They must be allowed the time to do their work and have food available to survive.

Many denitrification devices on the market, besides being overpriced do not function properly, and the bacteria must be fed on a regular basis. They are hard to keep adjusted and do not allow adequate time for the natural occuring bacteria to form and do their thing.

For convenience to the operator, many denitrification devices have evolved that do not require the addition of additional food for the bacteria. They were usually sold as coil-denitrators. But the inherent problems associated with all designs of that type were constant clogging and constant adjustments to the system.

As coil-denitrators are so easy and inexpensive to make, I am including those plans as well.

Part 2 - Basic Construction Notes for all functioning denitrators:

To make things as simple as possible, I will use the standard rate of one drop per second, 60 drops per minute as many denitrifiers are designed.

At this flow rate, the recommended time, converted to distance of travel for ease of calculation, for the system to function properly is 78 continuous feet of airtight enclosure. If the continuous distance is broken into cells the distance can be as little as 50 feet continuous, without the necessity of feeding. Any distance less than 50 feet, will require feeding.

The simplest method, albeit the most troublesome form of denitrification, is simply a coil-denitrator, using airline tubing as the active element. An alternative is a thin flat-denitrator of 1/4 inch double skinned polypropylene sheeting.

To make the unit less troublesome, 3/8 to 1/2 inch size tubing or the structured polypropylene sheeting should be used, in lieu of airline.

Note: If you already own a manufactured denitrator, that requires feeding. You may use two back to back and quit feeding or substitute the nutrient for the denitrator with simple hummingbird feeder mixed at the same proportions and use as equivalent nutrient and rate recommended by your manufacturer.

Before the denitrified water re-enters your aquaria it should be reoxygenated which is just allowing air to get to the last leg of the journey back to your sump. It also allows, any stray bacteria to be killed.

Part 3 - Coil Denitrators:

Most of the manufactured coil denitrators I have seen, were designed more for looks, than for proper operation. Those of you that have seen a functioning denitrator of any type are aware that the looks go out the window just as soon as the unit becomes active.

A coil denitrator consists of 5 or 6 components; The outer container, the coil & sleeve, a reoxygenation chamber (which can also double as the coil sleeve), a directing tube and the exit tube.

Keep in mind that we need a minimum of 50 feet of continuous tubing. You can build two units and run them back to back to meet the 50 foot requirement, should you elect to use larger diameter tubing, for ease of maintenance.

Since we are talking about low-cost units, I will describe the cheapest way to go, you can elaborate on that and use whatever other materials you may procure.

To build the cheapest unit, the equipment required consists of;

To construct; Take the bikers drinking cup and drill a hole in the bottom the same size or a little smaller than the straw or tube. Push the straw into the bottom of the container, until it is just 1 inch from the cap. It should fit very snug. Cut the exposed straw off about 1/4 inch above the bottom of this bottle.

Now take the other straw and place it in the lid, like you would for drinking purposes, but keep the bottom of the straw about 1/4 to 1/2 inch away from the bottom of the bottle, secure with polyethylene tape or silicone. Also, if there is an airhole in the cap, cover both sides with polyethylene tape or silicone. Leave the straw long, uncut.

This completes the construction of the re-oxygenation chamber and coil sleeve assembly. View below.

     ________::____    Directing Tube 
     :       ::   :
     :   ::  ::   :
     :   ::  ::   :    Bottle
     :   ::  ::   :
     :   ::  ::   :
     :   ::  ::   :                 RE-OXYGENATION CHAMBER
     :   ::  ::   :
     :   ::  ::   :
     I:  ::      :I    Cap
         ::            Exit Tube

Leaving a pigtail about a foot long, begin by taping the airline tubing close to the bottom of the bottle with polyethylene tape.

Proceed winding the airline tubing around the bottle to form a coil from the bottom to 1 inch above the cap. The gap at the top is for about three years of sediment to accumulate.

The plans for using a sleeve over the tubing are not shown in this unit.

If you would like to use a sleeve, the spacing between the turns should be an equivalent size to the tubing used, like as if you wound two tubes and then removed one. If you plan on using a proper fitting sleeve, the winding is from the cap end to the bottom of the bottle. The bottom is then sealed so that you have a continuous flow from the tube between the windings and exiting at the cap end. It is not easy using bottles, but if you are using acrylic materials the extra effort is worth it for the added flowrate of fourteen to twenty drops per minute, plus or minus.

The final part of the construction, consists of placing this unit inside of an inverted wide mouth jar, or taking a two-liter soda bottle and cutting it in half near the bottom. With the top facing down, place the completed re-oxygenation chamber, cap down, inside the soda bottle. The straw should exit the neck of the bottle and the cap of the bikers bottle should be siliconed heavily to the soda bottle neck, or to the cap of a wide mouthed jar if utilized.

Drill a hole in the bottom of the soda bottle, previously removed, through this hole place the pigtail from the coil. Fit the bottom of the bottle to the top half so that only about 1/2 to 1 inch of space is above the bikers bottle bottom. A little heat applied to the top half of the soda bottle will cause it to contract so that the bottom will slip on easier. If you chose to use a wide mouth jar, your home free, drill a hole for the exit tube, install the lid and your done.

Soda bottle users, use silicone between the layers of soda-bottle where it fits back together, plus place a piece of polyethylene tape around the seam to hold it securely.

              _____-----     -----_____        Bottom of Soda Bottle
              :    __________::___    :
     OOOOOOOOOOOOOO:         ::  :    :        Bottom of Bikers Bottle
              :    :     ::  ::  :O   :
              :   O:     ::  ::  :    :        O represent tubing coil
              :    :     ::  ::  :O   :
              :   O:     ::  ::  :    :
              :    :     ::  ::  :O   :        Seam and tape with
              :   O:     ::  ::  :    :        polyethylene tape.
              :    :     ::  ::  :O   :
              :   O:     ::  ::  :    :
              :    :     ::  ::  :O   :
              :   O:     ::  ::  :    :
               :   :     ::  ::  :   :
                :  :     ::  ::  :  :
                 : I:    ::     :I :
                  :------::-------:            Cap of Bikers Bottle
                   :     ::      :
                    :    ::     :
                     :   ::    :
                      :  ::   :
                        I:: I
                        -::-                   Cap of Soda Bottle

Now drill a hole in the soda bottle cap so that it will fit over the exit tube and screw the cap on. Your project is complete. If you chose to use a two unit system, the output from unit one is fed to the input of unit two.

A simple airline valve is used to control the flowrate at 7 to 10 drops per minute.

See further operating and maintenance instructions below...

Part 4 - Flat Block Denitrators:

The construction of the Flat-Block Denitrators is actually much easier than the coil type shown above, provided you can get the double skinned sheeting required for their construction. If not, you may have to build the unit entirely from scratch, a project that I would not like to embark on.

Since I am a cheapskate, I will tell you where you may possibly get the material for free, or for under about 20 bucks. It will take some work and coercing, but its usually worth it, when you find out that the material is almost unavailable in a single sheet without paying about 50 bucks extra to get a single sheet shipped to you.

Before I start on the construction, lets view some of the double skinned sheeting available.

I prefer a product called EXOLITE, which is a double-skinned polycarbonate structured sheeting. Next in line is LEXAN, a double-skinned acrylic sheet. Both come in approx 1/3 and 5/8 inch thicknesses. On the low end, are POLYFLUTE and COROPLAST polypropylene double-skinned sheeting. They only come in 1/4 inch thicknesses and have the same inherent problems as using airline tube with clogging and flowrate control.

Both Polyflute and Coroplast will take up much less space, if you consider 1/4 inch flat sheeting as space wasters. Usually one thickness of the thin sheeting is required for a good unit. The thicker Exolite and Lexan, usually require two or sometimes three thicknesses to get up to the required 50 feet of continuous ducting. But then you are only talking about a denitrator that is about 24 inches by 20 inches by 1-1/2 inches thick.

Many aquarists construct a unit that is as wide as the base their aquarium is sitting on and affix it to the back, which consumes less than 1 inch of space. The standard width of polycarbonate structured sheeting is 47-1/4 inches.

The number of vertical columns is directly proportional to the thickness of the material, the columns are square, and the dividers are usually the same thickness as the individual layers of sheeting material. If you go with the full 47-1/4 inch width of the sheeting, only one section about 20 inches tall will be required. If you prefer to build your unit to a width of about 24 inches, you will need to stack two sheets back to back. If you want your unit only about 12 inches tall, you may wind up with a unit that is three sheets thick or about 1-1/2 inches thick, ideal for hanging on the back of your aquaria.

Where to get polycarbonate structured sheeting:

Now for the fun part, you want cheap don't you? Take a Sunday drive and watch for greenhouses, you know, where they raise plants and stuff. Usually, newer greenhouses with aluminum frames have some type of covering other than glass, not all, but many use double skinned sheeting. If you are fortunate, they will have several pieces left over from when they built the place that are really too small for them to use to replace any broken panels that they might have. Cut off ends, etc., you get the picture!

For our use, it really doesn't matter whether the piece they have left over is too narrow or to short, all we need is a piece about 2 foot square out of the 47 inch by 9 foot original piece. Or whatever dimensions you are contemplating.

Now to be coercive, if you are a student, you almost have it made!

Introduce yourself as a student of (name your school), if you are not alone you could say (We) are in the need of a small piece of EXOLITE for a project we are working on. You are not misrepresenting yourself, just by naming your school, if you have a pal with you, we was used in the plural meaning me and my pal here, who are working on a project. This approach, although, unethical, is not untruthful, and will usually yield the piece for free and the owner of the greenhouse will usually be much more cooperative.

It might be a good idea, to research your project and the materials required before hitting on the first greenhouse you come to. Look at the material on his greenhouse. Is it thin or thick? Is it clear or whiteish? Does it look like cheap Coroplast or the better Exolite or Lexan, which is crystal clear. Check out the widths used on his greenhouse and the number of columns of the material. With a little quick calculations you can figure out just the size piece you need for your project. Then approach the owner. It would be wise to offer him about 20 bucks for the piece, that way he may be more interested in digging out a piece for you. But I would save that to see if at first he seems a little reluctant.

Now that you have your piece of Exolite or other double-skinned sheeting in hand, lets take a look at how simple it is to make the denitrator. It can be built without ever touching any glue whatsoever. I know because I had one running for almost 4 years that was only taped together, it never leaked once.

From the end, a piece of EXOLITE looks something like this:

     : : : : : : : : : : : : : : : : : : : : : : : : : : :

Well I can't get the lines close enough together, but you get the picture, its just a row of little square boxes. 47-1/4 inch wide by either 1/3 inch or 5/8 inch thick. The number of boxes is determined by the thickness of the material. The length of the material can be anywhere from 9 feet to 35 feet long, depending on the size ordered by the greenhouseman. But we only need a small piece of this!

Sitting vertically the piece would look similar, like a bunch of square tubes stacked next to each other.

     : : : : : : : : : : : : : : : : : : : :
     : : : : : : : : : : : : : : : : : : : :
     : : : : : : : : : : : : : : : : : : : :

The drawing capabilities of this program leave much to be desired!

Oh well, the idea is to form the ends of the plastic sheeting to make a continuous channel. This is accomplished by snipping a V shaped grove with a pair of sidecutters in every other channel separating the sheeting.

Don't cut the face or back. Nor the end pieces!

View looking at edge of a single internal column that was cut with a sidecutters.

                               :  :
                               :  :

These cuts are made on alternating rows and adjacent rows at the bottom. In other words, the water must flow down one column, up and over the next column, down that column and up the next where it goes over the top into the column next to that, etc. I hope you get the pix...

If you have better means at your disposal than a side cutters, by all means use it. The hole at the top and bottom rows can be as large if not larger than the size of the square. I use a little Dremel saw to cut mine out.

The last column of your denitrator will form the re-oxygenation chamber, or if you desire the last three rows can be utilized. Nothing special is done, other than an airhole is drilled at the top of the last column and the exit tube is placed in the end about 2 inches up from the bottom so the falling water can churn a little inside the last tube.

If you decide to use the third tube from the end, cut the divider between the second and last tube down as far as you can reach, about 2 to 3 inches would be ideal. You can even add an airline if you wish, but I wouldn't use an airstone, because you wouldn't be able to change it when it clogs.

The input to the unit is at the top of the first column, usually from the side, and the output is tubed over to the sump, from about 2 inches from the bottom of the last tube.

If you decide to use back to back stacked units, DO NOT make an oxygenator column on the back unit, also, exit the water from the top of the last column not the bottom, so that it will feed directly into the top of the front first column. When you use a double unit, the input and output are at the same end of the unit, which is very handy in most installations.

The water enters the back unit at the top and exits the front unit at the bottom. They are connected at the top at the other end, the back to the front using tubing. Or if your good at construction, by drilling and sealing with silicone, the proper columns at the face and back of the top of the required columns.

The unit must be airtight in order to function properly, except for the input pigtail and the exit tube. The simplest way to achieve this is to cut a piece of plexi or scrap from the piece you have and secure it to the bottom. You can get by with the tape alone, but sometimes you may get one channel draining into another, which is not good...

The best way naturally is to use plastic joining techniques, but us cheapo lazy guys, just cut a piece of plexi for the bottom and another for the top. Put a good coat of silicone on the plexi and set the denitrator in place over it. After the silicone is dry, we go back and put a piece of polyethylene tape over the top and bottom for structural strength to hold the whole thing together. Silicone will let go and make a prime mess, so always use the polyethylene tape.

I purposely spell out the words polyethylene tape, for a reason, its the only tape that will hold and never let go. It is UV protected and made for wet use. Not meaning wet when you put it on, use it on a dry surface and it won't let loose when wet. The Cajun Cook would say, I garrunnteeee it!!!

You shouldn't have any trouble finding this tape, the proper generic name is CT Polyethylene Tape, its about 12 bucks for a 100 foot roll or 3 bucks for the little hardware store size rolls. I have seen it at Central Hardware, Handy Andy, Tru-Value and even Grandpa Pidgeons. You may have to look over in the aisle where window coverings are sold. As this type of tape is designed for sticking plastic to plastic, plastic to metal and plastic to wood, for outdoor use. It's good stuff!

Since Exolite and Lexan, etc. denitrators are just a long tube in disguise I don't think any other pictures, or my attempt at drawing is necessary.

You may use an airvalve to control the water flowrate using a small airline tube for the pigtail. If you glue a piece of hard plastic tube in the inlet for affixing a pigtail, something like an air connector, you will be able to replace this little tube about once a year without any difficulty. Naturally the exit tube should be of a larger diameter, like 3/8 inch tubing so you don't get a clog from debris that will break loose from within the denitrator unit from time to time.

Part 5 - Operating Notes:

Connect your pigtail so that it receives water from your aquarium via the overflow recovery tank (surface skimmer) or anywhere after the pre-filter. You can run with the flow rate wide open until either unit is filled with water, then check to see if you can maintain a flowrate of one drop per second.

You may have to move your unit lower or closer to the sump area of your system to get it to flow properly. Once you are able to establish a flow rate of 1 drop per second, turn the unit off for two or three days to start the oxygen depletion within the unit. After two or three days of sitting idle, but before you start the unit up, place five little grains of regular sugar (or hummingbird food if you have it) into the pigtail tube, clamp it off so you don't get more than a bubble or two of air inside the tube, then reconnect and start the system.

To speed up the initial cycling process, you may want to run the unit at 1/2 flow rate for about two to three weeks, 30 drops per minute. Then increase the flow rate to the normal 1 drop per second.

It may take up to two months for the unit to become totally operational, however, don't be alarmed at the seemingly high reading of the effluent, which during cycling may show almost pure nitrite as an effluent, remember you are concentrating everything. A newly started system, if readings taken from the effluent will show an enormous amount of ammonia, which will decrease and the readings will show an enormous amount of nitrites, again, this will be followed with what appears to be a reading well over 140 of nitrates. These readings of the effluent are normal and will not upset the balance of your aquaria. The proper way to read the effluent of a denitrator is by regular water tests of your aquarium's water. Not by reading the effluent from the denitrator.

Once the denitrator is completely cycled, nitrate measurements may be taken at the output of the denitrator and the drip rate slowly reduced, by never more than one drop per minute, until a reading of zero nitrates is given by your test kit. Perfect adjustment is obtained when increasing the drip rate by 1 drop per minute shows a slight nitrate reading with the test kit. The test should not be performed for two days after any adjustment to the unit is made. Never reduce the output driprate below the exact count as measured above to insure that no hydrogen sulfide is produced.

If you are using the flat polycarbonate or acrylic denitrators, you can watch for signs of efficiency and adjust your flowrate upwards as needed. The facultatively aerobic/anaerobic bacteria will form a black area in the denitrators, if this black area seems to be pretty far from the re-oxygenation chamber, you may increase the flowrate, just a little at a time, until the black or active area is within 4 columns of the re-oxygenation chamber, the last two columns of the denitrator unit. Once the bacteria are established, even though they may grow to reach the re-oxygenation chamber, slowing down the effluent will not cause this area of the denitrator to clear up. Whatever flowrate was required to reach maximum efficiency should be noted and always use that flowrate with your particular unit.

Flowrate is counted only at the exit of the denitrator, not at the input, it is possible that the input can be as much as double as the output, due to vacuum in the drip reader if you use one. A drip reader is useless on a denitrator, because it will always fill up with water after a couple of weeks anyhow.

Special Note: Never let the denitrator dry out or run out of water. In the even of a long electrical outage, it is better to shut the unit off than to let it run dry. If you should come home and find that the unit ran out of water for some reason or other. Simply add five grains of sugar to the pigtail and restart the unit at the proper flowrate. Never, Never, Never up your flowrate or you will kill the facultativily aerobic/anaerobic bacteria, if the unit ran dry, humidity in the unit, once restarted should maintain all the bacteria colonies within the unit. Even a unit of either type, that ran dry, should still have plenty of water in the re-oxygenator part of the system to hold the humidity in and keep any further oxygen from entering once restarted.

If you have any questions, please e-mail me at (see /home/ page for current e-mail address) and please be specific in your questions if you want specific answers.

All of the units depicted, work exceptionally well, and I have built and used each one with great success. (At the time this page was updated in 2010, I have built well over 50 flat panel and over 100 coil denitrators!)

The units using airline tube or the smaller polypropylene double skinned sheeting will clog up and stop working after a year and a half or so. Or if a lot of debris is introduced to the system. A little jolt of water from your water pump will usually get them flowing again, but don't introduce too much oxygenated water to the denitrator in the process.

The larger units usually work totally maintenance free for years.

If you are fortunate enough to have a continuous nitrate reading below about 4ppm in your aquaria, it would be wise to introduce about one or two drops of regular hummingbird feed mixture, into your pigtail about once a month. Again, keep the airbubbles down to a minimum when doing this.

Those of you who have higher nitrate readings in your tank, will never have to feed your denitrator. In fact, you may want to consider building a second unit to handle the excess nitrates.

One last thing I want to stress is the importants of water changes. A denitrator does just that, removes nitrates, it does nothing for any other of the contaminants in your aquarium. Phosphate levels should be monitored more often and/or a strict regimine of water changes practiced.

Part 6 - How the unit works:

A denitrator is a very simple device, and sometimes bio-media is added to the first four or five columns of the flat-denitrator types, to produce a larger bacteria colony for the nitrosominos and nitrobacter to do their thing.

Basically, as the water follows its journey through the system, the beneficial bacteria colonizes and begins to work. I don't need to get into how a wet/dry works, but the principle is the same for the first part of your denitrator. As the flow continues and oxygen is depleted, other beneficial bacteria take over, they are neither aerobic nor anaerobic, they are facultatively aerobic/anaerobic, commonly called nitrate respirators, sort of in limbo, not very technical but who cares. Once the oxygen is exhausted, this section of the denitrator becomes anaerobic and then these little bacteria guys take over and eat the nitrates produced by the aerobic bacteria in the preceeding stages. It is beneficial to have as much facultatively aerobic/anaerobic bacteria as possible. That is why you adjust your denitrator so that these little guys populate almost to the end of the line.

There is one bad part about denitrators, their effluent is hydrogen sulfide, if I remember my chemistry right. One of the purposes of the re-oxygenation part of the unit is to not only kill the anaerobic bacteria that escapes the system, but also to burn off much of the hydrogen sulfide. In a properly flowing system, you shouldn't notice any hydrogen sulfide, if your system is running way to slow, you will notice and smell it, like an old rotton egg. In such a case, you can increase the flow just a tad. The addition of an air supply to the effluent before introduction to the tank is also beneficial.

Usually the effluent from a denitrator is fed so that it goes through the sump and/or protein skimmer before being reintroduced to the tank. The only reason for putting it through the protein skimmer is for oxygenation. If your sump has a large surface area and your wet/dry is above the water line and the water splashes into the sump, the effluent can be put directly into your sump.

Thanks for bearing with me, I may have repeated myself several times, messed up on the grammar quite a bit and wore your eyeballs out with the reading, but the systems are good and work just great.

Respectfully submitted,

Gary V. Deutschmann, Sr.

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