Pool Chemistry Calculator
A test kit gives you six numbers and no order to fix them in, and the order is where most wasted chemicals go. Put in what you tested and this works through it the way I would at the pool: unsafe water first, then alkalinity, pH, calcium and stabilizer, and the chlorine target last.
Every amount scales with this. Not sure? Use the volume calculator first.
Sets the calcium range
Your test results
Leave blank anything you did not test.
Total minus free, if your kit tests it
Sets your chlorine target
For the saturation check. 80°F if blank
What you have on hand
The percentage is on the bag
Result
Enter your pool volume
Only the numbers you enter are used. The gray ones in the fields are examples, and anything left blank stays out of the plan.
A test kit gives you six numbers and no order to fix them in, and the order is where most wasted chemicals go. Put in what you tested and this works through it the way I would at the pool: unsafe water first, then alkalinity, pH, calcium and stabilizer, and the chlorine target last.
Getting an accurate answer
- Leave a field blank if you did not test it. Nothing is worked out from a number you did not give, and the plan names what is missing and why it matters.
- Add one product at a time with the pump running, and let each circulate before the next. Never mix two products in the same bucket, and keep acid well away from chlorine.
- The doses are for liquid chlorine, 31.45% muriatic acid, baking soda, soda ash, calcium chloride and granular stabilizer. For tablets, cal hypo or dichlor, use the chlorine dose calculator, because each one adds stabilizer or calcium this plan does not count.
- The plan is for outdoor pools. Indoor pools and spas run stabilizer far lower, from none to about 30 ppm, and the chlorine targets here assume an outdoor level.
Why the order matters
The numbers on a test kit move each other, so fixing them in the wrong order means fixing some of them twice. The balancing guide sets out the order this follows, and the reasons are short.
Unsafe water comes first. Free chlorine at or near zero, green water, or combined chlorine over 0.5 ppm outranks everything else, because the rest is about comfort, cost and surfaces and this is about health. Before a shock, pH comes down to about 7.2, since chlorine works faster there.
Alkalinity before pH. Alkalinity is what holds pH in place. Set pH first in water at 200 ppm of alkalinity and it drifts back within days. Every acid lowers both, which is why the plan works out what the alkalinity dose does to pH before it doses pH at all.
Calcium and stabilizer late, chlorine last. Neither calcium nor stabilizer comes back down without draining, so they are set carefully and once. Stabilizer decides how much chlorine you need, so the chlorine target waits for it.
Where the targets come from
Free chlorine is a share of stabilizer, not a fixed number: about 11.5%, inside the 10 to 15% band, with 7.5% as the floor. At 40 ppm of stabilizer that means holding about 4.5 ppm, and at 80 about 9. Why it scales that way is worth five minutes.
pH aims for 7.5, inside 7.4 to 7.6. Alkalinity is raised to 80 when it is under 70 and lowered to 100 when it is over 120, so each dose lands inside the range with room to spare, since a drop test reads alkalinity in steps of 10 ppm.
Calcium is raised to 300 on plaster and 200 on vinyl or fiberglass, near the low end of each range, because the only way back down is replacing water. Stabilizer aims for 40 on a chlorine pool and 70 on a salt pool, the middle of 30 to 50 and of 60 to 80.
Last comes the saturation index, worked out for the water as it will be after the plan. Every number can sit in range while the water as a whole still attacks plaster or scales a heater, and this is where that shows.
The two doses no other calculator here makes
Calcium chloride and stabilizer are worked out from their molar masses, the same way the alkalinity doses are, rather than copied from a chart.
Calcium chloride. A mole of it, 110.98 g, adds one calcium, which a hardness test reports as 100.09 g of calcium carbonate. So one pound of pure calcium chloride raises 10,000 gallons by about 10.8 ppm. At 94% that is about 0.98 lb for every 10 ppm, and at 77% about 1.2 lb. Check the percentage on the bag and choose the matching one.
Stabilizer. Cyanuric acid is reported as itself, so there is nothing to convert: one pound in 10,000 gallons, about 37,850 liters, raises it about 12 ppm. That makes 10 ppm about 13 oz.
Both go in slowly. Calcium chloride heats the water as it dissolves, and stabilizer can take several days to dissolve and show fully on a test, which is how people end up adding it twice.
When the plan looks wrong
A dose looks huge. Check the volume first. Every amount scales with it, and it is the number most owners inherited rather than measured. The volume calculator takes ten minutes with a tape.
It says to raise chlorine that looked fine. The target moves with stabilizer. At 80 ppm of stabilizer, 4 ppm of chlorine is under the 6 ppm floor, however normal it looks on the kit.
pH lands low after the alkalinity acid. That is expected, and the plan says to aerate rather than add soda ash, which would put the alkalinity straight back. Why the two move together.
The readings came from strips. Strips are fine for a quick pH check and poor for alkalinity, stabilizer and chlorine above about 5 ppm. A plan is only as good as its readings, and a drop-based kit is the fix.
Questions about this calculator
What order should I add pool chemicals in?
Chlorine first if it is at or near zero or the water is green, then total alkalinity, then pH, then calcium hardness, then stabilizer, and the everyday chlorine target last. Alkalinity comes before pH because it holds pH in place, and chlorine comes last because stabilizer sets how much you need.
Can I add all my pool chemicals at the same time?
No. Add one at a time with the pump running, and let each circulate before the next. Never mix two products in a bucket, and keep acid and chlorine well apart: together they release chlorine gas.
How long should I wait between adding pool chemicals?
Long enough for the first to circulate, a few hours with the pump running, and a full turnover before you retest, which is 6 to 10 hours on a variable-speed pump. Stabilizer is the slow one: it can take several days to dissolve and read accurately.
What should my pool chemical levels be?
Free chlorine about 11.5% of your stabilizer reading, pH 7.4 to 7.6, total alkalinity 70 to 120 ppm, calcium hardness 250 to 400 ppm on plaster or 175 to 275 on vinyl and fiberglass, and stabilizer 30 to 50 ppm, or 60 to 80 on a salt pool.
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