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Why have CYA in a chlorine spa?


DougA

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Thanks for this very helpful post.

Why is it recommended to have any CYA in a hot tub if it reduces effectiveness of chlorine?  

What is the best level of CYA to maintain in a hot tub.  I've seen 20 or 30?  

I use Spa Choice Diclor which the ingredients say is 55.5% available chorine.  How much of this diclor would I need to add to my tub to get it to 30 PPM?  

Thank you very much!  Doug

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basically, a small mount of CYA makes the chlorine less aggressive (such as fading swimsuits). Personally  would shoot for 30 ppm for the simple reason that it's the lowest that can be measured with most test kits using the 'disappearing dot'. Meters are notoriously inaccurate for this test until you get into VERY EXPEN$IVE ones.

If you want to add CYA by using dichlor there is an easy way to get you in the ballpark. For every 10 ppm FC added by dichlor you are adding 9 ppm CYA so keep track of all the chlorine you have added using dichlor and when the total amount adds up to about 33 ppm FC added you should be right around 30 ppm CYA.Just  track your dichlor usage. For example, when you first fill you add enough dichlor to shock at 10 ppm and then need to add enough dichlor on a daily basis to raise your FC by 2 ppm to maintain it at 4 ppm (2 ppm daily chlorine loss). When you have added 33 ppm total in chlorine with dichlor then switch to bleach so you don't add more CYA.

Another way to look at it is that each 1/4 teaspoon of dichlor will raise 100 gallons approx. 2 ppm or slightly below so if your spa is 400 gallons you would need about a teaspoon to raise the FC about 2 ppm.

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