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Re: Sources of PO4

Neil broke the list so I'm sending this on for him ;)  -Cynthia 

---------- Forwarded message ----------
Date: Fri, 04 Jan 2002 20:18:51 -0500
From: Neil Frank <nfrank at mindspring_com>
Subject: Re: Sources of PO4 

"Ben B" <benrx at naxs_net> wrote:
>I too think I am going to venture timidly into trying to put a little PO4
>into my tank.  I don't have the nerve though to use Schultz's flower stuff.

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.
It was the most convenient source of P that I could find, and because it
was already in the house, the price was right :-) Although the mix has
other plant nutrients (including Cu and other trace elements), I had to
check to see if I might overdose something I did not want. Not the case --
the MG is dominated by P.... at least relative to the nutrient requirements
of aquatic plants. For example when you add enough MG to bring P to 0.1ppm,
the corresponding additions of N, K, Fe and Cu are also +0.1ppm for N and
K, and only +0.001ppm for Fe and +0.0005ppm for Cu.... all will hardly be
noticeable. You may ask how a 15-30-15 produces approximately the same
concentrations for N, P and K. This has to do with the archaeic convention
for expressing the P and K in terms of their oxides (P2O5 and K2O). The
actual percentages of N, P and K by weight are 15%, 13.2% and 12.5%. 

Ben also said:
>I have used the calculation tabel on the Krib by Neil Frank (
>http://www.thekrib.com/Plants/Fertilizer/dosing.html ) ......   maybe we can
>talk them into adding some PO4 information to those.

Here are some dosing possibilities:

0.2 grams of MG (15-30-15) in 70 gallons of water will yield a Phosphorus
(P) concentration of 0.1ppm. [This corresponds to a PO4 concentration of
0.34.] I have not yet used higher ammounts. 
I like to keep my tanks P limited, which keeps my plant growth slow and I
think also contributes to my very red plants.  When I occasionally add my
slug of P, however, my plants start fizzing like alka-selzer tablets. It
also covers all the leaves with O2 bubbles which I dont really like.

For people without a gram scale, 2 grams of MG is approximately 0.5t (1/2
teaspoon). Another even more convenient way is to prepare a stock solution:
I dissolve 20 grams in 1L of water . I then add 10ml of the blue brew to 70
gallons. (No I am not concerned about the die).  
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.]  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. Of course fish food will also provide N and P
in a ratio of ~7 to 1, so the extra N may not be needed. Same about P. YMMV.