Home and Commercial pools are treating their pools for cryptosporidium by raising the chlorine levels up to 20 milligrams per liter and holding that level for eight hours while the pool is not occupied. This level and time should reduce any cryptosporidium by 99.9%. Other values of chlorine concentration can be used to achieve the same result. If lower chlorine levels are used, the time has to be increased. The chlorine level in parts per million (or milligrams per liter) multiplied by the time that the level is held in hours just has to be at least 160.
Examples are:
- 20 parts per million (milligrams per liter) for 8 hours 8 X 20 = 160
- 10 parts per million (milligrams per liter) for 16 hours 10 X 16 = 160
- 5 parts per million (milligrams per liter) for 32 hours 5 X 32 = 160
The pH level of the pool needs to be checked and maintained between 7.2 and 7.8 at all times. Sodium hypochlorite or calcium hypochlorite should be used to raise the chlorine level. Non-chlorine shock (potassium peroxymonosulfate) is not effective in killing cryptosporidium. Stabilized chlorine (dichlor or trichlor) should also not be used to raise chlorine to very high levels because the stabilizer might interfere.
It is recommend swimmers not use pools with chlorine levels over 5 parts per million. After the chlorine level has been held, it can be quickly reduced by adding sodium thiosulfate crystals or sodium sulfite (available at pool supply stores) to the pool and waiting for the chlorine level to come back to your normal level. The amount and procedure recommended on the product label should be used.
Most pool testing kits can only measure less than 5 parts per million. In order to measure amounts higher than 3 to 5 parts per million of the chlorine in your pool, you will have to dilute the pool water. To do a dilution:
- Add one ounce of pool water to a clean glass 16 ounce measuring cup
- Add chlorine free water up to the ten ounce mark (distilled water or other bottled water is chlorine free)
- Measure the chlorine level of the water in the measuring cup following the instructions for your test kit
- The chlorine level in the pool is ten times the level you found in the measuring cup
Examples:
If you find a chlorine level of 2 in the measuring cup, your pool would have 20 (2 X 10 = 20)
If you find a chlorine level of 0.7 in your measuring cup, your pool would have 7 (0.7 X 10 = 7)
If you use a bromine test kit, the amount you measure with your test kit needs to be twice the value you would measure with a chlorine test kit. For example, if you wanted to perform a treatment equivalent to 20 parts per million of chlorine for 8 hours, the level of the diluted water (from instructions above) measured with your bromine test kit would have to be 40 parts per million for 8 hours.
The estimated amount of chlorine you will need to add to your pool to raise it to the proper value can be calculated using this calculator.
If you use bromine (then you might already know this) you can raise the level of bromine by adding the amount of liquid or powdered chlorine that you determine from the calculator.
This calculator requires the use of Javascript enabled and capable browsers.
All you need to know before you get started is your water source's volume in gallons, what type of chlorine you are using (liquid and cal hypo) and your water source's current reading for the variable you're trying to adjust.
All calculated amounts are approximate. This is at best a close approximation based on data you supply. We are not responsible for any chemicals you add to your water source (pool, spa, fountain, waterfall, pond or other water location), or for any liability resulting from following the suggestions made on this web page. When in doubt, add less chemical than called for and re-test before adding more. For further information, please contact a water chemical expert.
In these calculators, the abbreviation PPM is for parts per million. The data entry range is the workable range for all values; the range for Volume (quantity) Of Water is 1 to 9,999,999 gallons. The range for Total Chlorine and Free Available Chlorine is 0 to 99.9 PPM.
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