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:
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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.
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etc. 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.
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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 can 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.
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