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i have been re-doing my dry fert regime... both in composition and amounts..... and have been thinking about adding additional N (without adding more K) to supplement what i provide thru weekly water changes. In the past i have used NaNO3 to supplement KH2PO4 and KNO3. This is not ideal since sodium nitrate adds unnecessary Na+, I am now considering urea and figured i would join this discussion.

Conceptually, urea is more appealing to me than NH4NO3 (as used by some products, like Amano's)... and maybe safer if overused, since it takes a few days for residual material to convert to NH4. Because i have choromines (NH2Cl) in my tap water, i am already providing some type of NH4 salt in potentially large amounts after a water change. The average chloramine concentration of Raleigh tap water is 3.5 mg/L!! I now live near the water treatment plant, so i expect my level to be on the high side. Adding prime breaks the NH4 chlorine bond and yields some type of ("detoxified")ammonium salt. So, a 50% water change can be provding a large amount of this stuff. No wonder the plants pearl like crazy (OK, some of that is due to dissolved gases :))

I came across this article which talks about fate of urea in the aquatic environment. http://www.cryotech.com/products/pdf/ureafate.pdf It says that "urea completely degrades within 4 - 6 at 20degC" (into CO2 and ammonium). Based on the 40ppm "allowable" levels for salminid species, there is a reason to be somewhat comfortable with dosing of 0.5mg/L as used by the previous posters to this thred. I previously recommended short term concentrations of NH4 not to exceed 0.1mg/L.
http://www.thekrib.com/Chemistry/ammonia-toxicity.html

Seems like urea (in dry form) can be used at higher levels than NH4. It also provides a little bit of CO2 :)
 
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