best way to shock a pool?

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best way to shock a pool?

Postby tan8856 » Thu 17 Jun, 2010 15:55


Ive just purchased a 15 foot above ground easy-up pool and am getting a bit confused over what chemicals i should add and when. Can someone give me a few pointers?

I live in England where it can be rather chilly even during summer so the pool will probably only be used once a week. Do I still need to check the PH and FC levels everyday and keep them within range?

How often do i need to add algaecide? Once a week? When things start to look green?

How often do i need to shock? What chemicals do i use to do this? The chlorine we are using is Stabilised Chlorine Granules (sodium dichloroisocyanurate dihydrate) and on the tub it says to shock with calcium hypochlorite. But ive heard that calcium hypochlorite is only for indoor pools. Also, when i shock do i need to get the level to 10ppm? That seems very high to me. My friend said that i can shock the pool simply by adding a large dose of the Stabilised Chlorine Granules and that calcium hypochlorite is unnecessary.

Also, when i backwash my sand filter how long do i let it backwash? Is 1 minute too little?

Thank you :)

chem geek
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best way to shock a pool?

Postby chem geek » Thu 17 Jun, 2010 19:21

Many of the answers to your questions may be found in the Pool School including the Beginners Guide for Seasonal/Temporary Pools.

Any source of chlorine can be used in any pool. It's the side effects that you need to be aware of. The following are chemical facts independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

The amount of active chlorine in the pool that does the sanitation, oxidizing of bather waste, and killing/inhibition of algae is proportional to the FC/CYA ratio when CYA is in the water. CYA does more than just protect chlorine from breakdown from sunlight -- it significantly lowers the active chlorine level in the pool. Fortunately, it doesn't take much chlorine to kill pathogens, though takes more to kill algae. See the Chlorine / CYA Chart for appropriate levels of chlorine at each CYA level.

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