poolchemistrycalc

Lower total alkalinity

Into 21,100 gal of water, add

36.09lb 16.37kg

HASA Dry Acid — sodium bisulfate, 93.5%. Total alkalinity from 180 ppm to 100 ppm.

Total alkalinity on one scale: the band 60–180, the ideal band 80–120, the reading now at 180 ppm, and an arrow to 100 ppm carrying 36.09 lb. reads now 180 ppm target 100 ppm ideal code 60 80 120 180 36.09 lb −80 ppm with HASA Dry Acid

Your pool

feet, the long side
feet
inches of water, not wall height
inches of water
what your kit reads
where you want it

The quantity, the drawing, every product row and every step on this page are worked again as you type.

At 21,100 gal

Every product that does this

One product here has a quantity, and it makes the whole change of −80 ppm on its own.
Product Add Also moves
HASA Dry Acid
sodium bisulfate 93.5% 		36.09 lb
16.37 kg		 amount not stated
pH
HASA Muriatic Acid
hydrochloric acid 31.4% 		no quantity — see the label amount not stated
pH

The HASA Dry Acid label says: “0.5 lbs for each 0.1 pH unit reduction per 20,000 gals of water”.

In steps, if you would rather

Split into 5 equal steps of 7.22 lb each: add one, run the pump, and test again before the next.

Every step also moves pH, by an amount no fetched source states, so no figure for it is published here.
To reach Total added
164 ppm 7.22 lb
148 ppm 14.43 lb
132 ppm 21.65 lb
116 ppm 28.87 lb
100 ppm 36.09 lb

Where the band comes from

Source Range
COMAR 10.17.01.45 A(2)
conventional pool 		60–180 ppm
COMAR 10.17.01.45 A(2)
spa or hot tub 		60–180 ppm

Pool and spa rules are adopted and amended state by state, and most of the ranges here are written for public pools. Confirm every figure against the code your jurisdiction has adopted and against your own product label.

Always dilute acid before it goes in: ten parts water to one part acid, into the water and never the other way round. Run the pump while you add it, and test again before you add any more.

Other adjustments

Updated October 2026

Sources and dates

Ranges are quoted from the code named beside them, product strengths from the manufacturer's own product page, each retrieved on the date shown.

This site publishes calculated water volumes and chemical quantities for home pool and spa owners. It is not a health, safety or professional service, and it does not replace the instructions printed on the product you are holding. Not affiliated with, endorsed by or sponsored by HASA, Pyrock Chemical, Pentair, Hayward, Sonoma Hot Tubs, the Centers for Disease Control and Prevention, or any state health department. Product names are the trademarks of their owners and appear here only to identify the strength of what is in the container.