The Dose Per 10,000 Gallons Factor Card

Why this matters

Almost every chemical mistake on a route is an arithmetic mistake made standing in the sun: a factor carried from the wrong product, a volume rounded twice, a target typed in as the change. The pool forgives some of it. It does not forgive calcium or stabilizer poured high, because neither comes back out without draining water. This card is the one formula every dosing card in the shop uses, plus the four non-chlorine factors, worked so you can check the method against numbers you trust.

The formula, and the one rule about rounding

DOSE CARD (factors per 10,000 US gal)

dose = (target - reading) x (gallons / 10,000) x factor
       round ONLY the final answer

product              factor               raises
-------------------  -------------------  ---------
sodium bicarbonate   1.4 lb per 10 ppm    TA
calcium chloride 77% 1.2 lb per 10 ppm    CH
cyanuric acid        13 oz per 10 ppm     CYA
salt (NaCl)          1 lb gives 12 ppm    salt

chlorine products -> Shock Dosing Standard table
muriatic acid (TA) -> Muriatic Acid Handling and Dilution
pH with acid       -> kit acid-demand table

Three terms, three separate things to get right:

• Target minus reading is the change you want, in ppm. Write both numbers on the ticket, not just the difference, so the next tech can see whether the target was sensible. Targets come from 'Pool Chemistry Quick Reference' and are not restated here.
• Gallons over 10,000 scales the card to the pool. A 15,000 gallon pool is 1.5, a 7,500 gallon pool is 0.75. The volume itself comes from 'How to Estimate Pool and Spa Gallons'; a dose is never more accurate than the gallons under it.
• Factor is product per 10 ppm of change per 10,000 gallons, except salt, which is stated the other way round (ppm per pound) because that is how salt is sold and handled: by the 40 lb bag.

Round only at the end. If you round the gallon ratio to 2 on an 18,000 gallon pool and the change to 20 ppm on an 18 ppm gap, you have stacked two roundings in the same direction and overdosed about 23 percent. Carry the full figures through and round the final pounds to what your scoop or scale actually reads.

Where each factor comes from

These are not lookup numbers someone picked. Each one falls out of the chemistry, which matters because it lets you check a product label that states a different strength.

• Sodium bicarbonate, 1.4 lb per 10 ppm TA. Total alkalinity is reported as ppm of calcium carbonate. Bicarbonate delivers one equivalent of alkalinity per 84 g, carbonate as CaCO3 counts 50 g per equivalent, and 10,000 gallons is about 37,850 liters. Ten ppm in that volume is about 379 g of CaCO3 equivalent, times 84 over 50, which is about 636 g of bicarbonate, or 1.40 lb.
• Calcium chloride (77 percent), 1.2 lb per 10 ppm CH. Calcium hardness is also reported as CaCO3. Ten ppm in 10,000 gallons is 3.79 moles of calcium; at 111 g per mole of calcium chloride that is about 420 g of the pure salt, divided by 0.77 for the 77 percent product, about 545 g, or 1.20 lb. The 94 percent anhydrous product needs about 1.0 lb for the same rise, which is why the bag strength gets read before the factor is used.
• Cyanuric acid, 13 oz per 10 ppm. Stabilizer is weighed as itself, so 10 ppm in 37,850 liters is about 379 g, or 13.4 oz. Use 13 oz for a pure granular product; a liquid stabilizer is sold by its own label strength and is dosed off that label.
• Salt, 12 ppm per pound. One pound is 454 g; in 37,850 liters that is 12.0 ppm. A 40 lb bag therefore moves 10,000 gallons about 480 ppm.

'Pool Chemistry Quick Reference' carries rounder rule-of-thumb rows for bicarbonate and calcium chloride (by the ounce, written for quick field use). Where the two disagree, dose from this card, because these factors are derived and the product strength is stated beside them.

Worked twice: alkalinity

An 18,000 gallon plaster pool. TA reads 70 ppm, the shop's target for this pool is 90 ppm.

• Change: 90 minus 70 is 20 ppm.
• Scale: 18,000 over 10,000 is 1.8.
• Factor: 1.4 lb per 10 ppm, so 20 ppm is 2 times 1.4, or 2.8 lb per 10,000 gallons.
• Dose: 2.8 times 1.8 is 5.04 lb. Call it 5.0 lb.

Second direction. Start from the product. Five pounds is 5 over 1.8, or 2.78 lb per 10,000 gallons. At 1.4 lb per 10 ppm, 2.78 lb gives 2.78 over 1.4 times 10, about 19.8 ppm. Seventy plus 19.8 lands at about 90. The units cancel the same way both times: lb per (ppm per 10,000 gal) times ppm times (10,000 gal units) leaves lb.

Sanity estimate. A pound and a half per 10 ppm on a pool a bit under twice the reference size, for twice the change, should be somewhere around 5 or 6 lb. It is. If the answer had come out at 50 lb, a decimal moved, and the estimate catches it before the bag is open.

How it goes in, and why a large TA correction is split across visits, belongs to 'How to Raise Total Alkalinity With Sodium Bicarbonate'.

Worked twice: calcium hardness

A 12,500 gallon pool on soft fill water. CH reads 150 ppm; the target is 250 ppm.

• Change: 250 minus 150 is 100 ppm.
• Scale: 12,500 over 10,000 is 1.25.
• Factor: 1.2 lb per 10 ppm, so 100 ppm is 10 times 1.2, or 12 lb per 10,000 gallons.
• Dose: 12 times 1.25 is 15.0 lb of the 77 percent product.

Second direction. Fifteen pounds over 1.25 is 12 lb per 10,000 gallons; 12 over 1.2 is 10 steps of 10 ppm, or 100 ppm. One hundred fifty plus 100 is 250. It closes.

What the bag strength would have done. Poured from the 94 percent product at the 77 percent factor, the same 15 lb delivers 15 times 0.94 over 0.77, about 18.3 lb of 77 percent equivalent, which is about 122 ppm. The pool lands near 272 instead of 250. Small, but it is in the direction you cannot reverse, and on a pool already near its ceiling it is the difference between balanced and scaling. Calcium chloride also heats the water it dissolves in, hard: it is pre-dissolved in a bucket of pool water, product into water, a portion at a time. The method and the reasons for splitting a correction this size belong to 'How to Raise Calcium Hardness With Calcium Chloride' and 'Calcium Hardness and Scale Management'.

The stabilizer and salt rows, and the trap in each

Stabilizer. The factor is easy; the timing is not. Granular cyanuric acid dissolves over days, so a same-day retest reads low and invites a second dose. On a 16,000 gallon pool going from 30 to 50 ppm the arithmetic is 20 ppm, so 2 times 13 oz, or 26 oz per 10,000 gallons, times 1.6, which is 41.6 oz, about 2.6 lb. That number is right. Retesting it the same afternoon and adding more because the turbidity test still reads 35 is how a pool ends up at 70. The dissolving and retest rule belongs to 'Cyanuric Acid Management Standard' and 'How to Add Stabilizer and Confirm It Dissolved'.

Salt. A 20,000 gallon salt pool reads 2,600 ppm and the cell's label asks for 3,200. Change 600 ppm; at 12 ppm per pound per 10,000 gallons, 600 over 12 is 50 lb per 10,000 gallons, times 2.0 is 100 lb, two and a half 40 lb bags. Check it back: 100 lb in 20,000 gallons is 50 lb per 10,000, times 12 is 600 ppm. The trap is the reading, not the math. Cell-reported salt drifts with temperature and plate condition, so the dose is sized off a test-kit or meter reading, and a cell that reads low after a correct dose is a cell question for 'Salt Cell Cleaning & Maintenance', not a reason to add another bag. Like calcium and stabilizer, salt only leaves by splash-out, backwash and dilution.

Why chlorine and acid are not on the card

Both are on other cards on purpose, and both have a feature this formula does not.

• Chlorine is sold in four common forms at four strengths, and each carries a passenger: stabilizer, calcium or salt. The per-unit strength table lives in 'Shock Dosing Standard', and the side effects in 'What Each Chlorine Product Does to the Other Readings'. A weekly liquid dose is sized from the week's loss, not from a gap to a static target; see 'How to Size the Weekly Liquid Chlorine Dose to Last the Week'.
• Muriatic acid lowers pH by an amount that depends on the alkalinity buffering it, so a fixed ounces-per-0.2-pH factor is only right at the TA it was written for. The pH dose comes from the acid demand test ('How to Lower pH With Muriatic Acid Using the Acid Demand Test'). The TA knockdown, which does follow a fixed factor, is in 'Muriatic Acid Handling and Dilution', along with the two product strengths that differ by better than a factor of two.

What changes the answer

• The strength on the label. Every factor above is for the strength named beside it. Read it off the container in front of you every time, because a shop that stocks both 77 percent and anhydrous calcium chloride will eventually load the wrong bag.
• The volume is a guess. An irregular free-form pool estimated at 15,000 gallons that really holds 18,000 under-doses every product by a sixth. When a pool keeps landing short of its targets by the same fraction across different products, the gallons are wrong, not the chemicals. Re-measure before you change any factor.
• Splash-out and fill water. A pool topped up heavily from a hard or soft fill source between visits moves its CH and TA on its own. Dose to the reading in front of you, not to last week's.

How to verify you got it right

Write the four inputs on the ticket in the same order as the formula (target, reading, gallons, factor) and the answer last. Anyone checking can redo it in ten seconds. Then retest only after the product has circulated through at least one turnover (granular stabilizer much longer). A retest that lands within the kit's own resolution of the target, typically one titration step, says the gallons and the factor were both right. Landing short by the same fraction on two different products says the gallons are wrong.

References

• See related: Pool Chemistry Quick Reference (targets), How to Estimate Pool and Spa Gallons
• See related: Shock Dosing Standard (chlorine product table), Muriatic Acid Handling and Dilution (TA knockdown)
• See related: Cyanuric Acid Management Standard, Calcium Hardness and Scale Management, Salt Cell Cleaning & Maintenance
• Product labels and safety data sheets for stated strength, mixing and first aid