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Re:Plant tabs, PO4 and Miracle Grow (fwd)

---------- Forwarded message ----------
Date: Tue, 08 Jan 2002 23:16:15 -0500
From: Neil Frank <aquarian.subjects at mindspring_com>
Subject: Re:Plant tabs, PO4 and Miracle Grow

Tom Barr said:

>I do not think [Delaware Aquatic Plant Tabs] have NO3/NH4 or PO4.

When I had them tested many moons ago, I found they had N and P... dont
know what form. But you covered all the options above. 

>Neil wrote:
>> Ever since the discussion on PO4 additions started 1-2 years ago, I have
>> used Miracle Grow (the blue crystals) to occasionally supplement my tanks.
>So was it the NH4 and urea or the PO4 that helps your plants? Urea can be
>quickly converted in the presence of water and oxygen and bacteria into NH4
>and used.

GOOD QUESTION. I did not even notice that half of the N is from ammonium
phosphate. At least the NH4 concentration is only ~0.05ppm... which my
article on the KRIB says should be safe. 

>  Can you see what 1.0ppm of PO4 is like without problems associated
>with NH4/Urea? How about 2.0ppm of PO4?

Unfortunately, I dont feel it is wise to use MG for that purpose. The
corresponding ammonium concentrations is starting to look like toxic levels
(for fish).

>> The actual percentages of N, P and K by weight are 15%, 13.2% and 12.5%.
>So how much NH4 vs PO4 is there here? Try a .5ppm level of PO4 and a .4ppm

While 0.4ppm NH4 is not supposed to be lethal, it is uncomfortably high for
At pH 7 and 86deg, 1-hr concentrations should be < 12ppm and 4-day avg
value less than 0.7ppm. The plants should suck up the NH4 quickly and not
permit a long-term value to be close to 0.7. Nevertheless, I'll let you do
that experiment.

RANGE OF 1-2ppm. For those levels, use sodium biphosphate or potassium

>Plants have rough time using Urea. It needs broken down by bacteria. So
>there's some lag time before this used.

This is OK with me. I wasnt adding the small amount of MG for N anyway.

>But algae can use organic PO4 by using alkaline phosphatase that allows
>algae to use it and store it as a luxury nutrient where as the plants need
>bacteria to do the deed. So if adding inorganic forms of PO4 such as KH2PO4
>will even up the selection for the dynamics between algae and aquatic
>macrophytes. Algae can live up to 20 generations with a healthy storage of
>PO4 granules at absent PO4 levels. Your plants will be in sad shape and rot
>and decomposition of plant matter will add enough organic PO4 back into the
>system where the algae have the advantage. Adding inorganic PO4 may
>circumvent this process. Not sure but will look into the literature more.
>Sounds better than some of the other ponderables.

I am not sure I understood what you said, but please report back when you
have a more complete assessment.

>Although urea is an organic N fertilizer, it is rapidly converted to the
>ammonium form within a short time after exposure to aerated water and
>bacteria. Therefore, under most conditions urea acts more like inorganic
>ammonium fertilizers than like natural organic fertilizers. It's also cheap

Maybe urea is like time released ammonium. This might be a great source of
N in a heavily planted tank.... and might prove to be reasonably safe at
concentrations of up to a few ppm
>> To complement the P, I also add N and K in proportion to Gerloff's 1975
>> published "critical concentrations" for Elodea which Diana Walstad includes
>> in her book. The critical ratios of N:P:K are 11-2-8. [These are said to be
>> minimum concentrations needed for unrestricted growth.]
>Is using one species as a ruler good for all plants? 

I have to agree that one species is not the ideal ruler. But this was the
only critical concentration data that I had (from Diana's book). If anyone
has other quantitative info, it would be great to have.

Many plants are
>sensitive to low levels or need higher levels of PO4 , NH4 vs NO3 is another
>issue. Plants absorb P primarily as the H2PO4 - and HPO4 = ions which are
>predominant. The H2PO4 - ion is more readily absorbed than the HPO 4 = by
>most plants. In young plants, P is most abundant in tissue at the growing
>point. It is readily translocated from older tissue to younger tissue, and
>as plants mature, most of the element moves into the seeds and/or fruits.

It would be very helpful for you to document and publicize those plants
that "seem" to require different relative amounts of PO4. We all thrive on
such anecdotal evidence.

>> To provide the
>> extra N and K not available from the MG, I use nitrate of soda (NaNO3) and
>> potash (KCl). You can also use potassium nitrate (KNO3), but this does not
>> provide enough N by itself.
>Depends on what species of N. It does add enough NH4 for the tank.

Are you suggesting that the MG provides enough NH4?  If so, the tank would
still be lacking in N, absent other sources.

>I have considered making stock solutions of ammonium sulfate so I can
>explore the independent effects of NH4+, NO3 and PO4.

Why bother with ammonium sulfate. Why not use liquid ammonia (from grocery
store). I believe it becomes NH4+ at pH in our tanks. Chemists, please

 I have looked at it
>from the dry additions but have not come to any recommedable amounts yet.
>Cost is very cheap for ammonium sulfate also, 4$ for 25lbs.
>I know what happens at slightly higher levels of NH4 that persist for any
>length of time. Algae. It's fine if the NH4is very low and the plant growth
>is dense and fast/healthy.

I agree. The one time I experimented with adding NH4 to my tanks, I quickly
produced green water.