I’m trying to decipher and expand upon a formula in this paper about water and pool chemistry, however the formula apparently assumes information I don’t have. I don’t know if the constants are calculated from something in the paper, general chemistry or are assumptions of industry standards I can’t find. I’m unable to find contact information for the author and the Journal is basically dead.

The paper is:

Swimming Pool and Spa Water Chemical Adjustments; John A. Wojtowicz, Chemcon, Originally appeared in Journal of the Swimming Pool and Spa Industry, Volume 5, Number 1, pages 39–56.

(

http://jspsi.poolhelp.com/ARTICLES/JSPSI_V5N1_pp39-56.pdf)

The base formula is:

VMA = a + b(pH) + c(TA) + d(CA)

Where…

VMA = the volume of 31.45% muriatic acid (HCL) in fl oz to add to 10000 gallons of pool water to reduce its pH to 7.2

a = unknown constant

b = unknown constant

pH = Current pH of the 10,000 pool (between 8.2 and 7.

c = unknown constant

TA = the total current alkalinity (ppm)

d = unknwn constant (perhaps a derivative of density aka specific gravity)

CA = cyanuric acid (ppm)

The functional example is:

VMA = –237.34 + 29.894(pH) + 0.244(TA) + 0.1276(CA)

The formula works to observed data. However, I can’t figure out where the constants for a, b, c, and d actually come from either from the paper or by trying to reverse engineer the formula.

A CLUE: in the paper that author makes the statement, “The required quantity of acid [to add] is readily calculable from the decrease is calculated total alkalinity [TA] at the new pH. Each mol of added acid

neutralizes one mol of total alkalinity.”

So, a later formula for calculating the change in TA when adding Muriatic acid is:

(delta)TA = (fl. oz HCL acid added) x 29.57 x d x p x 1000 x 50/ (EW x V x 3.7854)

Where…

29.57 = conversion mL per Ounce (29.57mL = 1oz)

d = density (specific gravity) = 1.16 for Muriatic acid

p = purity or percent solution = 0.3145 for a 31.45% Muriatic acid solution

1000 = presumably conversion to liter

50 = unknown, perhaps existing concentration of Cyanuric acid as ppm in the pool as a stabilizer

EW = equivalent weight of -36.46 for Muriatic acid

V = total volume of pool = 10,000 gallons

3.7854 = conversion of gallons to liter (1Gal = 3.7854 L)

Any help greatly appreciated!!