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Re: [APD] dosing Fleet Enema..

Jason Reck wrote:

How much of this should I be adding to a 75gallon tank with 3wpg and CO2
injection.  I'm using the "Barr Method" of two or three doses a week of
KNO3, K2SO4, and TMG with a 50% water change every week. Actually I
guess rather than just telling me what to add, I'm curious how it breaks
down into ppm...Chucks calculator only includes dry KH2PO4, I think.

I had someone email me this question several months ago, here is a copy of my reply:


> I use a Fleet enema to dose PO4. I've searched the APD archives and
> found a reference indicating there is 7.5 mg phosphate per drop but I
> can't figure how this person arrived at that number. The bottle contains
> 118ml of solution containing 16 grams of monobasic sodium phosphate and
> 7 grams of dibasic sodium phosphate. Sodium content is 4.4 grams.

monobasic sodium phosphate
Molecular formula: H2NaPO4

dibasic sodium phosphate
Molecular formula: HNa2PO4

The molecular weights involved are:
H : 1.00794 g/mol
Na : 22.98977 g/mol
P : 30.97376 g/mol
O : 15.9994 g/mol

(monobasic sodium phosphate)
H2NaPO4 = 2 hygrogens, 1 sodium, 1 phosphorus, 4 oxygen.

when you add it up, 1 mol of H2NaPO4 = 119.977g.  Phosphate (PO4) =
94.97136 g/mol.   So, 79% of the weight of H2NaPO4 is phosphate.

(dibasic sodium phosphate)
HNaPO4 is almost the same, just missing one hydrogen
1 Hydrogen, 1 sodium, 1 phosphorus, 4 oxygen.

1 mol of HNaPO4 = 118.9691g. So, 80% of HNaPO4 is phosphate.

Back to your info:
118ml, containing 16 grams of monobasic, and 7 grams of dibasic.

So, in 118ml, you have 12.64g of phosphate from the monobasic,
and 5.6g of phosphate from dibasic.  (79% and 80%).

So, in 118ml, you have 18.24g of phosphate.

Each ml would then contain 0.155g of phosphate, or 155mg.

> I've searched the APD archives and found a reference indicating
> there is 7.5 mg phosphate per drop

I don't know how many drops there are in an ML, so it's impossible
to be sure of that number.  If there are twenty drops per milliliter,
then that would right on.  155mg in one ml, 155/20 drops = 7.75mg

I'll leave it to you to count the drops in one ML, or you can just dose
by ML....


Note, it's possible the monobasic sodium phosphate will have 2
H2O attached to it (dihydrate), so that would alter the percentages

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