same dose
RecommendedDosing Is Always Per 10,000 Gallons
Every pool chemical dose in common use is written per 10,000 gallons of water. That is the unit on the bag, the unit in the dose charts and the unit used below. Scaling to an actual pool is one step: divide the pool volume by 10,000 and multiply every listed dose by that figure. A 19,100 gallon pool has a multiplier of 1.91, so a dose listed as 1.5 lb becomes 2.87 lb.
This makes accurate pool volume the foundation of accurate dosing. A volume that is wrong by 25 percent makes every dose wrong by 25 percent, forever, in the same direction. Measure the pool once and keep the number.
These are estimatesDose figures are calculated from product strength and pool volume. They are not a substitute for testing. Always test the water first, dose from the measured reading, then wait and retest before dosing again.
Target Ranges
Balanced water is water sitting inside all of these ranges at the same time. Chasing one reading while ignoring the others is the usual reason a pool stays difficult.
ReadingTarget rangeRaise it withLower it with
Free chlorine1 to 3 ppmLiquid chlorine or cal hypoTime, sunlight, partial drain
pH7.4 to 7.6Soda ashMuriatic acid or dry acid
Total alkalinity80 to 120 ppmSodium bicarbonateMuriatic acid or dry acid
Calcium hardness200 to 400 ppmCalcium chloridePartial drain and refill
Cyanuric acid30 to 50 ppmStabiliser (cyanuric acid)Partial drain and refill
Dose Rates Per 10,000 Gallons
These are the working numbers behind the calculator. Each one assumes the stated product strength, so check the label, since liquid chlorine in particular is sold at several concentrations.
GoalProductAmount per 10,000 gallons
Raise free chlorine by 1 ppmLiquid chlorine, 12.5 percent10.7 fl oz
Raise free chlorine by 1 ppmCal hypo, 73 percent2 oz
Raise total alkalinity by 10 ppmSodium bicarbonate1.5 lb
Raise calcium hardness by 10 ppmCalcium chloride1.25 lb
Raise cyanuric acid by 10 ppmStabiliser0.85 lb
Raise pHSoda ashDose by test result, add in small steps
Lower pH or alkalinityMuriatic acid or dry acidDose by test result, add in small steps
Worked example
A 19,100 gallon pool tests at 0.5 ppm free chlorine and the target is 2 ppm. The gap is 1.5 ppm. At 10.7 fl oz of 12.5 percent liquid chlorine per ppm per 10,000 gallons, the dose is 10.7 x 1.5 x 1.91, which is 30.7 fl oz, so just under a quart.
The same pool tests at 60 ppm total alkalinity and the target is 90 ppm, a gap of 30 ppm. At 1.5 lb of sodium bicarbonate per 10 ppm per 10,000 gallons, the dose is 1.5 x 3 x 1.91, which is 8.6 lb.
Test Before Dosing, Every Time
The single most useful habit in pool care is refusing to add anything without a current test result. Water chemistry moves with rainfall, bather load, sunlight, temperature and top-up water. Last week's reading is not this week's reading.
- Use a drop based test kit or test strips that are in date. Strips that have been sitting open in a damp shed read badly.
- Collect the sample elbow deep, away from returns and away from the skimmer, so it represents circulated water.
- Test free chlorine and pH at minimum before each dose. Test alkalinity, calcium hardness and cyanuric acid monthly, or after any large water addition.
- Record the readings. A short log makes it obvious whether a problem is drifting or sudden.
Order Matters
Adjust in this order: total alkalinity first, then pH, then calcium hardness, then chlorine and stabiliser. Alkalinity buffers pH, so correcting pH before alkalinity means the pH will drift straight back. Once alkalinity is inside 80 to 120 ppm, pH becomes far easier to hold at 7.4 to 7.6.
Note that acid lowers both pH and alkalinity together, and soda ash raises both. There is no product that moves one without touching the other, which is why balancing takes several passes rather than one.
How to Add Chemicals Safely
Pump running, always
Add chemicals with the circulation pump running and leave it running for at least a few hours afterwards. Chemicals added to still water sit in a concentrated layer, which bleaches liners, etches plaster and gives a false reading at the far end of the pool.
Never mix chemicals
Do not mix pool chemicals with each other, in a bucket, in a scoop, or in the skimmer. Chlorine and acid mixed together release chlorine gas. Different chlorine types mixed dry can ignite. Use a separate clean container for each product, or better, dilute each one separately and add them to the pool at different times, several hours apart.
Acid into water, never water into acid
When diluting muriatic acid, always pour the acid slowly into a bucket of water. Pouring water into acid causes a violent exothermic reaction that can spit acid out of the container. Wear eye protection and gloves, work upwind, and pour close to the water surface to limit splashing and fumes.
Distribute, do not dump
Pour liquids slowly around the perimeter in front of a return jet. Pre-dissolve granular products in a bucket of pool water where the label allows it, then pour that solution around the pool. Cal hypo and undissolved granules dropped straight in will sit on the floor and bleach whatever they land on.
Wait and Retest
Give a dose time to circulate before judging it. Chlorine and acid need at least 4 to 6 hours with the pump running. Alkalinity increaser needs 6 to 12 hours. Stabiliser is slow and can take several days to fully register, which is why stabiliser is the chemical most often overdosed by people who retest too early and add more.
Retest, then dose again if needed. Half a dose twice is always safer than a double dose once, because the only ways to bring cyanuric acid or calcium hardness back down are partial draining and refilling.
Overshooting is expensiveChlorine burns off and pH can be pushed back, but excess cyanuric acid and excess calcium hardness can only be diluted out by draining and refilling. Dose conservatively on those two.
Common Situations
- Cloudy water with normal chlorine. Usually filtration or high calcium and high pH combined. Check pH and hardness before adding more chlorine.
- Chlorine that will not hold. Often cyanuric acid far above 50 ppm, or a heavy organic load. Test stabiliser before assuming the chlorine is at fault.
- pH climbing constantly. Common with new plaster and with high alkalinity. Lower alkalinity toward 80 ppm and pH usually settles.
- After heavy rain. Rain dilutes stabiliser, calcium and alkalinity and adds organics. Test the full panel, not just chlorine.