[APD] RE: Fe and optimizing the substrate

[Jeff Ludwig <jeff at rockytop_net>]

> There is a simple test to see this NO3=> N2 occur in anyone's planted 
tank.
> Remove the plants and keep out in a tub/bucket etc for a 2-3 weeks or 
a
> spare tank.
> Leave the substrate in the tank, use a small tank such as ten gal or 
5 gal
> so there's less plants to deal with storing while this is being done.
> Add KNO3 and measure the loss of NO3 over a week, then see how week 
no#2
> does and then week 3#.

There is an even easier way, but I'm lacking a key piece of 
information... do a nitrogen balance.  Simply save your clippings over 
a month or two, dry them, weight them on a good analytic balance (I do 
have access to one, so I could do this for those local to me)...  What 
I am missing is an estimate of nitrogen in plant tissue on a _dry 
weight_ basis. It would be important to return the tank to the same 
state of "pruned" to get a good result.  If lots of us do this, 
systematic errors involved will be averaged out quite a bit and should 
give decent agreement.  But lets be realistic here, we're looking for 
an order of magnitude effect, this should be very apparent if it is 
occurring...

The problem with removing plants to check: At moderate levels of oxygen 
you have the 2NO3->N2+3O2 reaction occurring, to keep consistent with 
the marine folks that do deep sand beds call this region the anoxic 
region.  At even lower oxygen levels, call this area anaerobic, you 
have the 2NO3- + 11H+ -> 2NH4+ + 3H2O reaction occurring (opposite of 
biofiltration).  Removing the plants may drop the overall oxygen 
concentration in the substrate and favor a reconversion to ammonia  as 
opposed to nitrogen gas, so if anything removing the plants might be 
considered a low limit to denitrification... see latest issue of FAMA 
Re: Plenums in marine tanks for more discussion about this... Deep sand 
beds that are too anaerobic turn into nitrate factories.

Jeff Ludwig
Elkton, MD

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