Calculate how much cal-hypo (65% / 68%) to add to raise Free Chlorine (FC).
Enter your values and press Calculate. Inputs are saved on this device.
This calculator estimates how much calcium hypochlorite, or cal-hypo, is needed to raise Free Chlorine from the current level to your target. Enter the pool volume, current FC, target FC, and the percentage printed on the product label. The result is shown in pounds and ounces.
Use an accurate pool volume and select the actual product strength. A 65% product and a 73% product do not deliver the same amount of available chlorine.
Cal-hypo adds chlorine without adding cyanuric acid, but it also adds calcium. That can be useful in water with low calcium hardness, but regular use may create problems in pools that already have high CH or hard fill water.
Because cal-hypo is a strong oxidizer, it must be stored dry and away from acids, trichlor, dichlor, oils, and other chemicals. Never combine products in a feeder, bucket, scoop, or storage container.
Cal-hypo can be used for routine chlorination or for raising FC quickly when the pool’s calcium level can tolerate it. It may not be the best long-term choice for pools with high calcium hardness, scale problems, or frequent evaporation and refill.
No. Cal-hypo adds chlorine and calcium, but it does not add cyanuric acid.
Yes. Repeated use gradually increases CH, which can raise the risk of scale when pH, alkalinity, or water temperature are also high.
Follow the product label. Some products permit pre-dissolving, while others direct you to broadcast the granules. Never use a contaminated bucket or scoop.
Yes, when an extra chlorine dose is needed and the water’s calcium balance can tolerate it. The salt system itself still produces chlorine during normal operation.
Before making cal-hypo your regular chlorine source, check your calcium hardness and CSI. The chlorine may solve today’s problem while the added calcium quietly builds tomorrow’s scale problem.