Why We Shock Our Pools
When we shock our pools, we are essentially “super-oxidizing” the water and burning off organics and chloramines.
When to Shock
When the level of total chlorine exceeds the amount of free chlorine by 0.2 ppm or more, it’s time to shock. Free chlorine is the good stuff; it’s chlorine that is waiting around for a mess to clean up. Bring on your sunscreen, sweat, dirty feet…free chlorine can handle it.
So why is your “total chlorine” higher than your “free chlorine”? When chlorine cleans up after those dirty feet, left-over chlorine molecules remain in your pool. Just kind of floating there, taking up space and smelling bad. These chlorine molecules are called “combined chlorine” or “chloramines”, and they account for the difference between total chlorine and free chlorine. We want them out of the pool!
How to Shock
Easy! While there is a tiny bit of math involved, it’s a super easy calculation. Let’s consider the following as an example to help us understand the concept.
Hypothetical Water Test Results:
- Total Chlorine = 3.0
- Free Chlorine = 2.5
- Combined Chlorine = 0.5
We’re only including total and free chlorine here to illustrate their role in arriving at combined chlorine. Combined chlorine is the number we are concerned with. We simply multiply combined chlorine (0.5, in this case) by 10 to obtain our recommended chlorine shock dosage in PPM.
0.5 x 10 = 5 PPM.
Based on the above readings, we need to increase our chlorine level by 5 PPM in order to effectively shock our pool and eat up the combined chlorine. Caution: Almost is not good enough here. 4.8 PPM just won’t cut it. If we don’t hit the magic number of 10 times combined chlorine, we will not hit “breakpoint chlorination” and we may as well have not added any chlorine at all to our pool. In fact, failing to hit combined chlorine times 10 could leave your water worse off than you began!
Chlorine Dosage Calculator – The Shockulator
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