# Re: Dosing calculations...

• To: Aquatic-Plants at actwin_com
• Subject: Re: Dosing calculations...
• From: Paul Sears <psears at nrn1_NRCan.gc.ca>
• Date: Sat, 21 Feb 1998 19:39:38 -0500 (EST)
• In-Reply-To: <199802202048.PAA00651 at acme_actwin.com> from "Aquatic Plants Digest" at Feb 20, 98 03:48:20 pm

```> From: "Dixon, Steven" <stdixon at bechtel_com>
> Subject: Dosing Calcs KH2PO4
>
>
> So I'm trying to work out how to dose my 125 gal. aquarium in the range
> of 0.1 ppm phosphate.
>
> I figure my aquarium has 110 gals of water in it.  Since a gallon of
> water is 3.785 liters, I should have about 416 liters of water in the
> tank.  Dividing 1000 liters by 416 = 2.4; so 1 g of stuff dissolved in
> my tank with 110 gals of water should yield a concentration of 2.4 ppm.
> Right?

Yes.

> figured that potassium
> phosphate monobasic is about 70% PO4 by weight.  (95 weight of the
> phospate divided by 136 the weight of the whole molecule = 70%).  So 1 g
> of KH2PO4 should yield 1.68 ppm of phosphate in my tank.  Right?

Yes.

> Dividing by 20, 0.05 g of the stuff should yield 0.084 ppm phosphate --
> which is fairly close to where I want to start dosing.
>
Yes, again.

> So roughly I figure I need to add about 1/2 of the 0.1 g spoon to my
> tank.  How does that sound?  Any comments on the starting dose?

That sounds pretty good to me.  I think the amounts I'm using are
similar, but I must confess that the precision of the chemistry I use on
my fish tanks leaves a bit to be desired; I tend to say "That looks about
right." and throw it in.

I would do the calculation:

110 U.S. gallons is roughly 400 L.
400 L of water weighs 400 kg
To get 0.1 ppm, I need 400 kg divided by 10^7
That is 0.04 g of phosphate
KH2PO4 is 70% phosphate, so divide 0.04 by 0.7
I make it about 0.057 g of KH2PO4

i.e., the same result.  This method is a little more direct, I think,
though in essence it is the same.

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