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  1. Nitrex Box
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (Thu, 3 Sep 1992)
  2. DIY Coil Denitrator
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (Mon, 11 Oct 1993)
  3. DIY coil denitrator - cheap
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (Mon, 26 Apr 1993)
  4. Coil Denitraters
    by () (14 Feb 1994)
  5. Denitrification Explained- Don't Bother
    by (Jay Cheroske) (Wed, 09 Mar 1994)

Nitrex Box

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: Thu, 3 Sep 1992
Newsgroup: alt.aquaria

On a related subject, does anyone have a working version of a coil
denitrator?  If I understand the principle, it sounds pretty simple:
run water very slowly through a long, thin tube.  Aerobic bacteria
at the source end do their normal NH4->NO2->NO3 thing, using up the 
oxygen in the water in the process.  Anaerobic bacteria can then 
flourish in the rest of the length of the tube, reducing nitrates to 
N2 gas.  

How long should the tube be, how thin should it be, what kind of water 
flow is needed, should the outflow be filtered, etc, etc.

I think I remember someone in netland was building one a while back. 


DIY Coil Denitrator

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: Mon, 11 Oct 1993

The basic coil denitrator is a long section of small diameter tubing
with a slow flow of oxygenated water containing ammonia, nitrites and
nitrates, i.e., normal aquarium water.  Aerobic bacteria naturally
colonize the insides of the tubing and transform ammonia to nitrite
and nitrite to nitrate.  This process uses up the dissolved oxygen in
the front section of the coil and produces anaerobic conditions in the
rest of the length.  Anaerobic forms of bacteria grow in this area
and reduce the nitrates and nitrite to gaseous nitrogen.
The trick in the setup is to pick the correct tubing size and length
and proper water flow such that enough bacteria of the right type can
develop and have enough time to complete the denitrification cycle.
Safety and efficiency concerns direct the actual design of such a

The coil is simple to make from readily available materials.  A visit
to a hardware store or nursery that carries drip irrigation supplies
will provide you with the basics.  Fifteen to twenty-five feet of the
thin-walled black, 1/4" PVC tubing used for drip irrigation is perfect
for this application.  Simple connectors are available that allow you
to attach the tubing to a source of water.  This will generally
produce too much water flow but an inexpensive 1-4 gallon per hour
(GPH) valve is also available that allows for fine adjustments of the
water flow.

For optimum operation, the water should be mechanically but NOT
biologically filtered before entering the coil.  This prevents
water-born particles from clogging the small diameter features of the
coil while supplying the maximum amount of ammonia and nitrite to the
aerobic bacteria.  Unfortunately, this is difficult to accomplish in
practice since any mechanical filter media will also become a
substrate for nitrifying bacteria.  A good compromise is to use the
water return of a canister or trickle filter as the source of water.
This water is very clean yet has been proven to provide enough "food"
for the bacteria.

For safe operation, the outflow from the coil should be passed through
a biological filter of some kind.  At some point during the startup
period of the denitrator, enough bacteria will be present to reduce
nitrate to nitrite but not enough to take it all the way to gaseous
nitrogen.  It is also possible that after being established, something
may happen that would disrupt the denitrification cycle and nitrites
could again be generated.  You do not want to return this nitrite
laden water directly to the aquarium.


Two of our large 90 gallon freshwater aquariums are heavily planted
and well stocked with fish.  Even with the lush plant growth, we had
to change significant amounts of water to maintain low levels of
nitrates.  Prior to implementing the coil denitrators, we were
changing 50% of the water every two weeks.  This was time consuming
and quite expensive due to the water conditioning and plant fertilizer
products that we use.

Both of these aquariums have trickle filters which allowed a very
simple coil denitrator system.  A hole was punched in the vinyl water
return line to the aquarium with an inexpensive drip irrigation hole
punch designed for this purpose.  The water return line passes over
the trickle filter sump at the point the hole was punched so if any
leakage occurs it will harmlessly drip into the filter.  A 1/4" right
angle connector pushed into the hole connects one end of the coil to
the return line.  The back pressure from the 4 foot head is sufficient
to provide more than enough flow through the coil.

The small 1-4 GPH valve is put at the outlet end of the coil.  The
valve clogs easily so it is best to put it on the outlet side of the
coil for easy periodic cleaning.  A short piece of 1/4" tube is
attached to the other side of the valve and fits into a small hole
drilled in the filter drip tray cover.  The water from the coil thus
passes back through the trickle filter providing insurance against
toxic nitrites.  The coil outlet is a loose fit in the cover so it can
be easily removed for cleaning and monitoring water flow and nitrate

The coil itself rests on the PVC plumbing coming from the filter pump.  
It is not fastened down so it can be easily moved if access to the 
plumbing is required. 

Once set up, the water flow through the coil can be measured by timing
how long it takes to fill a container of known size.  For example, if
it takes 6 minutes to fill a 500 ml container, the water flow is 5
liters per hour.  Water flow should be checked regularly since
bacteria and their waste products will build up and restrict the coil
and valve.  The valve can easily be removed and cleared by blowing
through it but the coil should be left undisturbed.  We have found
that the flow through the coil itself is usually not impeded enough to
affect the operation and any attempts to clear the tube will probably
result in a disruption of the denitrification cycle.

The system takes 4-6 weeks for the aerobic and anaerobic bacteria to
completely populate the coil.  Prior to this point you may find some
nitrite being formed if you have a sensitive test kit.

Once the coil denitrator is established, the nitrate reduction will 
depend on the flow through the coil and what percentage of the coil
contains anaerobic bacteria. 


In our set up, we use 15 feet of 3/16" ID tubing and have a water flow 
of 3 liters per hour through the coil.  The most recent nitrate test
with a Lamotte low range nitrate test kit showed 1.0 ppm
nitrogen-nitrate (4.4 ppm nitrate) on the input and 0.75 ppm (3.3 ppm)
on the output.  With a reduction of 1 ppm (1 mg/l) and a flow of 3
l/h, the denitrator is removing 3 mg of nitrate per hour.  This is
keeping up with nitrate production since the overall nitrate levels in
the aquariums are staying at around 4-6 ppm.  There is no nitrite
coming from the coil as verified by a Lamotte nitrite test kit.

Note that the effects of the denitrator can only be seen if the
nitrate concentration of the inlet water is very low since the
resolution of test kits available to the hobbyist varies with the
nitrate levels.  For example, it is simple to tell the difference
between 2 and 3 ppm but almost impossible to tell the difference
between 19 and 20 ppm.

The effectiveness of the coil denitrator has allowed us to reduce the
amount of water we change by two thirds with the attendant reduction
in the cost of water conditioners and stress to the fish.  The ten
dollar investment is paying large dividends in both time and money
saved and in overall water quality improvements.

George L. Booth                   Founding Member, The Colorado Aquarium, Inc           __          Aquatic Gardener's Association
Software Development Engineer     /  \  /\          Colorado Aquarium Society
Manufacturing Test Division    /\/    \/  \           Rainbowfish Study Group
Hewlett-Packard Company       /  \/\  /    \/\             Modern Aquascaping
Loveland, Colorado  _________/    \ \/      \ \___x__________________________

DIY coil denitrator - cheap

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: Mon, 26 Apr 1993

George does DIY.  Who would have believed it? 

I set up an experimental coil denitrator this weekend and thought I would 
describe it to the net. 

My concept is that denitrifying bacteria will spontaneously grow in an
anerobic environment with the right conditions.  As an alternative,
nitrifying bacteria can switch to denitrifying bacteria if the
conditions are right.

I have a length of PVC tubing with a small inside diameter.  If I
provide a slow flow of clean water in the tubing, nitrifying bacteria
will grow.  The nitrifying bacteria at the beginning of the tube will
use up oxygen in the water as part of their conversion process.  In
theory, at some point in the tube all the oxygen will be depleted and
denitrifying bacteria will form.  These bacteria will then reduce the
nitrates to gaseous nitrogen.

The only trick is to find the correct water flow, tube diameter and
tube length to provide the correct surface area to water volume ratio.

I arbitraily used a 15' length of 3/16" ID PVC tubing.  This is
connected to the tank return line from my trickle filter with drip
irrigation hardware.  I found a Rainbird valve that is adjustable to 1
to 4 gallons per hour at the local hardware store.  It is running wide
open.  A simple punch makes a small hole in the 3/4" return tubing and
the valve plugs into the hole.  A barb on the valve prevents leaks.
The water from the end of the tube drips back into the trickle sump.
When I change water, I will turn the valve off so that air does not
get into the tubing.  The coil of tubing sits horizontally so nitrogen 
gas can easily escape (if it works!).  

I used clear PVC tubing so I could see what happens, if anything. 

The valve was $0.49 and the special hole punch was $2.79.  You can get 
drip irrigation tubing at the same source that is really cheap and
opaque to boot.  

I don't expect to see any results for 4-6 weeks.  It will take 2-3
weeks to get nitrifying bacteria to form and some more time for 
denitrifying to form (if they do).  

I will monitor the output water for oxygen content.  If I see it drop,
I will start to check the nitrates on the input and output side to 
see what happens. 

Stay tuned for future results. 

Coil Denitraters

by ()
Date: 14 Feb 1994

md064291-at-longs.LANCE.ColoState.Edu wrote:
> 1) How well do they work?

We have two that are removing 1 mg/l at a rate of 3 liters
per hour (3 mg nitrate per hour).  I have recently increased
the length of the coil to get more reductuion.  

> 2) The flow rates that I've seen are very slow (45-60 
> drops per minute!). Is this practical to use in-line 
> with a return line to the tank or are they intended to 
> filter small amounts of water slowly (in a sump for 
> example) independently from the main water return line.

They are far too slow to be used inline.  Ours tap off the 
water return line and then drip back into the sump. 

> 3) Does the diameter of the of tubing matter?  Is the 
> goal to have small radius tubing in order to compact as 
> much length as possible into the space allowed? Or does
> it really matter?

You want the maximum coil surface area to water volume so it
seems reasonable to have a small diameter coil.  However, if
it's too small, it will clog easily (the bacteria produce 
waste products and they don't live forever).  Around 3/16"
ID seems to be working hwell for me. 

> 4) There seems to be quite a bit of wasted space in the 
> interior of the filter where there are no "coils".  
> Couldn't you use multiple coils to get more surface area?  
> Or could you maybe fill the interior with some sort of 
> media (bio-balls?) so that the de-oxygenated water could 
> pass upwards through it before leaving the filter?  
> This seems like it would provide a greater opportunity 
> for nitrates to be removed.

I have 50' of 1/4" PVC drip irrigation tubing laying in the cabinet.
It's wound into a 4" diameter clump so it doesn't take up much
space.  The commercial coils seems space ineffcient just to 
make it look fancy (and worth the high price charged). 

> Is anyone using one of these things?

I am.  :-). 

George L. Booth                   Founding Member, The Colorado Aquarium, Inc           __          Aquatic Gardener's Association
Software Development Engineer     /  \  /\          Colorado Aquarium Society
Manufacturing Test Division    /\/    \/  \           Rainbowfish Study Group
Hewlett-Packard Company       /  \/\  /    \/\             Modern Aquascaping
Loveland, Colorado  _________/    \ \/      \ \___x__________________________

Denitrification Explained- Don't Bother

by (Jay Cheroske)
Date: Wed, 09 Mar 1994

It's really sad that such a simple issue has become so tangled and
convoluted, but I'll admit right off that it's easy to become confused when
the industry makes money off of people's confusion. In a nutshell,
DENIRIFICATION IS BU-at-%#*IT. It's not worth the trouble or the money to try
and set up a denit filter. Many people would have you believe there is no
way to remove NO3 from a tank without resorting to biological reduction.
This of course is totally wrong.

There are three ways to remove nitrate from a tank: 1) Use denitrification
to reduce NO3 to N2 gas, via anarobic bacteria, which then bubbles out of
your tank, or 2) Place some higher plants or macroalgae in your tank, which
will take up the NO3 and sequester it (it can then be harvested), or 3) Set
up an algal scrubber, which will remove NO3 from the water more effectivly
than the previous two.

The problem with denitrification is that it's a pain to set up, you're not
really sure it's doing anything, strange stuff can come out of your denit
filter if something goes wrong, and finally, the water that comes out of
the filter is almost totally depleted in O2. Just think what the RedOx
level of that stuff must be!!!

Higher plants and macroalgae work good except that they have a tendency to
take over your entire tank. I would recomend placing your plants on a rock
that is easially removed so that when you harvest the stuff you can see if
it's starting to spread. Remove the rock and pull off any strands that have
attached themselves to other rocks. This method is very effective at
removing NO3 and has the added benefit of adding O2 to your tank, which
raises RedOx levels.

Lastly we come to the mighty algal scrubber, the most effective filter in
the world. I'm not going to describe a scrubber--there are plenty of good
books with lots of info, but I will say that no filter offers the benefits
of a scrubber with the ease of use. During they day the scrubber lights can
be turned off because RedOx levels are higher during the day.
Photosynthesis by plants (and in the case of a reef tank, corals and other
symbionts) raises RedOx levels. At night, RedOx levels typically fall
significantly because there is no photosynthesis taking place. This where
the scrubber really shows its beauty--the scrubber is turned on opposite
the tank lights so that there is no drop in RedOx levels overnight. Your
stuff never has to deal with a period where conditions are

In my opinion there are two types of aquarists out there-- those that
prefer to set up a balanced system that basically takes care of itself
without the use of such things as ozone, strange filter medias, CO2
injectors, controllers, etc., and those that feel that in order to maintain
an aquarium, every factor that can be controled externally should be
controlled externally. Just check out the "high-tech reef system" in Moe
for an example. The industry loves this second type because they can sell
him/her all these useless gadgets and charge an arm and a leg for them. The
downside of this is that a) many people spend money on things they do not
need, and b) it makes people outside the hobby view it as an expensive and
complicated pursuit, and scares them away. As for which method works
better, a look at our dying planet should tell you-- whenever mankind tries
to improve on mother nature he always screws things up.

I've bought lots of stuff that I wish I'd never purshased (XNitrate for
one) and don't want other hobbists to waste their money on things they do
not need. Reading a FAMA usually provides me with a small amount of useful
info and a lot of frustration because I see so many ads for products that
are basically useless.

<flame on>

The following is not need in a reef tank:

trickle filter, carbon, poly filter, ozone, any other filter media,
controller, reactor, denit filter.

<flame off>

what is needed:

bright light, algal scrubber, protein skimmer (maybe), good live rock, good
tank plant growth, high flow rate, some type of sediment trap (could be 100
micron filter bag, sponge in overflow, gravel on bottom, etc.)

Now I just sit back and wait...


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This page was last updated 29 October 1998