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    * From: Neil Frank <aquarian.subjects at mindspring_com>
    * Date: Fri, 11 Jan 2002 18:06:49 -0500

>Neil Frank wrote:

> Paul, can you please clarify. 62 ppm nitrate is equivalent to what? Recall
> I only said a few ppm urea. This is coming from a person that only feels
> comfortable with 0.05ppm of NH4 and 0.1ppm of P. I was figuring that a
> concentration of urea > .05 should be OK. Question is how much higher than
> .05 (.1?, .5?, 1ppm?) . This all depends on how quickly it goes to NH4 and
> how quickly do the plants suck up the NH4. With a true slow release, there
> can be no residual NH4. BTW, I was not planning to dump in 43ppm!

I rechecked my calculations and found a mistake or two.  Actually I added
45 ppm urea, and I added that amount because it gives the equivalent amount
of nitrogen as a 1/10 dilution of Hoagland's nutrient solution, the
standard solution for supplying macronutrients when I did my research on
aquatic plants.  I grew my research plants in 1/5 strength Hoaglands, but
generally don't get my aquaria much higher than 1/10 Hoaglands.  The 45 ppm
supplies as much nitrogen as 93 ppm of nitrate (not 62 ppm).  That is
because urea is 46.6% nitrogen, whereas nitrate is only 22.5% nitrogen.  I
have had 93 ppm of nitrate in aquaria with no visible harm to plants or
animals, but the 45 ppm of urea killed all my Daphnia, and brought on a
green water takeover.  The conclusion is that you can safely load up the
water column with a lot more nitrate nitrogen than urea nitrogen, and that
you should regard both urea and ammonia as potentially damaging.  If you
like to make frequent, small doses, urea and ammonia will not harm things.
The all-purpose Miracle-Gro has all its nitrogen as either urea or
ammonium, and so it should be added in small amounts.  On the other hand,
if you are dosing with KNO3, you can add larger, less frequent doses.
Another nice thing about KNO3, is that you can test with a nitrate test kit
to see when it is all used up, and you need to add more.  A problem with
urea is that we don't have test kits for it.  I have tried the ammonium
test kit and it doesn't register urea at all.

Paul Krombholz, in warm central Mississippi, where the front that went
through was a dry front.