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>I took note of the suggestion to use an out-of-tank hydroponic filter as 
>one means of removing NO3 from aquarium water. Has anyone one designed an 
>out-of-tank anaerobic system for nitrogen removal? I can see some problems 
>that would have to be overcome but it sounds possible. Possibly a 
>deoxengenator on the input and return through an air reactor?

>Just a thought.

>Phil Bunch
>Lemon Grove, California

Phil, see Coil Denitrifiers.These have slow flow rates so you don't need to
worry much about adding O2 or removing it, the bacteria inb the coils do
that till there's no O2 left. Also batch denitifiers, these handle larger
volumes of water but are complicated and costly for a tank(they were about
400-700$ range).
Generally, too little NO3 is the issue for planted tanks.
This can be dealt with by KNO3 or fish waste(this is better for NH4 sources
A water change is also very easy and generally a good thing for many tanks
using CO2.

But if your tap water is high in NO3 etc I suggest a plant filter, rather
than a coil denitifier.
I am trying to think up a reason to use something like this for a planted
tanks would be of use.What is it for in relation to a planted tank? 
If you over stock, then it's a question of too many fish. Tap water NO3
seldom exceeds 40ppm. 

 Plants are quite good at the removal of NO3 and wetland plants are used
for this for wastewater treatment all over down here in FL.Wetland soils
are good denitrifiers. But onlky so much flow will flux in/out like the
coils. Coils work well and are relatively easy, more a Salt water thing
since they hate water changes due to salt cost(plain old tap water is
cheap). Adjusting the flow rate through these can be a problem. Clogging
etc. I think a simple plant filter, even some rock wool in the back of a
HOB filter works fine if you put a Peace lily in there. Emergent plants are
the best for what we want to do most often as aquarist and plants look
nicer than bacteria. Tunze sold the hydroponic plant filters many years
ago(still do along with Hydrologix still?) but the history goes much
further back to the first filters for tanks/ponds etc.
The planted tank it self is a plant filter. Why would you need tro remove
more NO3 and then add more for the plants? Even tap with 40ppm when a 50%
water change is done will only add another 20ppm which can be brought down
to roughly 0 in about a week depending on conditions, time for another
water change.
5-10ppm is nice, but reality is that you can push it further. Might not be
able to keep up with lots of Discus that are well fed a rich diet, but in
most cases it should be fine. But most folks do not have that issue with
the tap and the heavy bioload on top of it. Then a FW refugium is in order,
but, then you may as well put some of that bioload into another planted
tank or use faster growers. If you go down this circular path for all the
ends and outs, you'll end up going back to the plants for nutrient removal
needs. It's better for most all nutrient removal issues, FW, SW etc. 

Tom Barr

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