Urea

If you visit my blog on a regular basis you have probably come to realize I don't just accept what I have heard on the internet.   I was told that I should be cautious about using Urea because it will continue to transform into Ammonia over time and that I might create an Ammonia time bomb.  The reasoning was that the Ammonia I measured one day may continue to increase due to previous applications weeks before, and I might find my Ammonia levels on a fast track to disaster.

I have also been adding fresh urine which I was told would act the same way.  So I did a test
On Sept 6th I mixed a 1% Ammonia solution using Urea.  One week later I saw no appreciable difference.  Today 14 days later I found the Ammonia level to be 4%.  So I now believe that Urea will continue to create Ammonia over time.

Urea test in back on left / System water test on right.

But I have been using Urine and Urea for several months now and my tests have never had the Ammonia 'Time Bomb' happen.   It may be that the levels I'm adding everyday are exactly what is being converted to Nitrite.

My conclusion is that Urea and possibly urine will continue to create Ammonia, but I don't see this as a reason to age the solution before adding it to a functioning aquaponic system.   But killing pathogens which even though they are not very likely to be present is a good reason.   The proper way to use urine is to store it in a sealed container for about six months.  As it ferments and turns urea to ammonia the pathogens will die. This process is described in this article   http://www.goveganic.net/article217.html

I have also been asked why I felt it necessary to add Ammonia to an aquaponic system.  That after all is what the fish are for and it seems to many that it would be detrimental to the fish. I don't believe it is if the Nitrification process is converting all the Ammonia.  I add the Ammonia because I'm still growing my fish population and the fish load is currently not supplying adequate Nitrate for the plants.

Veering off topic I would also like to add this:
Balancing the fish load hence the food loading of the system is an important topic which I will cover one day. But in short, media beds will supply a much better condition for Nitrification than a raft system while also supplying a place to grow at the same time.  I personally like rafts better, and therefore condone the use of moving bed filters which to many seems to circumvent the purpose of aquaponics.  It's just another hybrid system that when compared to media beds (also considered hybrid) provides both clean water to the fish and Nitrate to the plants.  The only disadvantage I see is that a solids filter is also required.  Otherwise the roots will become dirty and suffer from a lack of oxygen..

UPDATE: 12/23/2012
I have come to appreciate the simplicity of a media bed. Besides offering nitrification a 3/4" gravel bed will filter solids which would otherwise cling to the roots of plants in the rafts.  As my fish population and their overall size grew so did the sludge.   Cleaning my filters became an overwhelming choir. For more see Filtering Poo with Continous Flow Media Bed