# Re: Can someone check my math?

<Aaron's original question>
>  > Is it acceptable to assume that 1 mL of this stuff then
>  > represents (1000 mg x 97% x 30%) or 291 mg of PO4?

> > > Also sounds good.

<Jerry's response>
> >>Concentrated Phosphoric Acid is much denser than water
> (approx. 1.8(?) for a 97% concentration) - a 30% sol. is approx.
> 1.2.  This means that unless your calculations include the
> differences due to the specific gravity and if you are using a volume
> measurement (ml), you'll be adding approximately 20% more
> phosphate than you think you're adding.<<

> Since you're using volumes, density _doesn't_ matter.

<My uninvited interjection>
I think the 30% concentration sighted for the "pH Down" product is
probably 30% *by weight* not by volume.

According to my ancient CRC Handbook, a 30% phosphoric acid solution
contains 354.1 grams/liter of phosphoric acid.  That also 354.1 mg/l.
Phosphoric acid is 97% phosphate, so the "pH Down" product would provide
343 mg/l of phosphate.

One ml of pH down in 343 liters of water would produce 1 mg/l phosphate.

Roger Miller