High CYA - Pool store said add shock


New member
May 11, 2021
Enola, PA
Moved from here.
My CYA is reading about 100 (with the strips)...maybe a little higher. I have to take a sample to the pool store to get a closer reading. I called them and was told that I can just use shock once a week (not to use the tablets at all) for about a month or so and with rain water and adding water to the pool due to evaporation and splash, it will start to come down. Is that true? My husband did NOT want this pool. I had him install it to draw the grandkids in so he will flip if I tell him we have to drain it after we just got it hooked up and running from winter. I see you said to use bleach. Do you mean normal household bleach? Is that better than the shock they recommended to use?
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Bronze Supporter
Mar 27, 2019
Pool Size
Stop going to the pool store and start using TFP as your pool bible. Read through the Pool School articles and get yourself a good test kit. The test strips are garbage but I do not doubt your CYA is way too high because that is a very common issue for new people just discovering this site. If your CYA is actually 100, you will need to exchange approx half of your water but you need to start testing yourself first. CYA increases due to excessive use of tri-chlor pucks so you must use those in moderation, if at all.

"Shock" is just powder Cal-hypo which the pool stores sell. We use bleach/liquid chlorine for regular use and you can buy it at HD, Walmart, or other locations. Do not use Chlorox laundry bleach. Also, please update your signature with info about your pool so others can help you better.

Test Kits Compared


Gold Supporter
Jun 28, 2017
Fresno, CA
Pool Size
If you willing to learn about your pool water and the TFP method you can have a safe pool for you and your grandchildren all for very little $. Your first investment is a quality test kit that you will have for years, see Andy's post above for the link about the quality kits recommended.



Bronze Supporter
May 11, 2018
"Shock" is chlorine. Chlorine can be dispensed by liquid chlorine (bleach), cal hypo (often referred to as 'shock'), or trichlor tablets. TFT prefers liquid chlorine because it doesn't add byproducts like calcium (cal hypo) or CYA (trichlor tabs). If you're new to this, stick with liquid chlorine. But first get a test kit like others here recommended and then they can walk you through balancing your chemicals.

My water is soft, so sometimes I add cal hypo to keep calcium hardness within range. Or if my CYA is running low, I'll switch to trichlor tabs for a few weeks. 90% of the time I use liquid chlorine.
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