Chlorine Block

[Melody Brutkiewicz]

We are having fits with the Chlorine reading. Our pool people say we are suffering from Chlorine Block. We were told to shock it with 10 bags of chlorine shock and run it for a week. The week is almost up and we are still not getting a chlorine reading. Now they say we need to shock it with 10 bags on non-chlorine shock. WE have a 15,000 gallon above ground pool with a sand filter.
Our readings are as follows

Free chlorine 0.1 ppm
Total chloein 1.4 ppm
pH 7.3
Hardness 80 ppm
Alkalinity 80 ppm
Cyanuric Acid 30 ppm

Can anyone tell me if we are getting sound advice. We are having friends here this weekend and would love to use the pool. It is crystal clear.

[chem geek]

Did you just open the pool after letting it go over the winter? Was the CYA level higher when you closed the pool? Sometimes soil bacteria will break down CYA into ammonia if a pool is let go. The ammonia will take a lot of chlorine to break it down -- 10x the ammonia level. You can get an inexpensive ammonia test kit from a pet/fish/aquarium store to see if that's the problem (and can then figure on how much more chlorine you'll need to add).

I'm concerned about your chlorine shock as it could be Dichlor which would raise the CYA level (for every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm). If the shock is Cal-Hypo, then that's OK since for every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm and your current CH is low (that's fine for a vinyl pool).

Richard

[pawmaw 50]

Since opening the pool, we have discovered that we have a chlorine block. This is an inground 15,000
gallon, vinyl liner, sand filte, chlorinating dispenser usin 3 inch chlorine tablets. We have had many pool
samples done and the last reading is free chlorine 0.4, Total chlorine 1.6, combined chlorine 1.1 ppm,
ph 7.1, hardness 190 ppm, Alkalinity 110 ppm, cyanuric acid 85 ppm, copper 0.03 ppm, iron 0 ppm. No
matter what we do, what chemicals we put in, we still end up with very little free chlorine. I've tried
shocking with 6 bags of zap it, another time 5 bags of zap it, 4 gallons of liquid chlorine. Although I have
been successful in getting the combined chlorine and total chlorine levels down, I have been unsuccessful
getting the free chlorine levels where it needs to be. Any help that you might be able to give would
sincerely appreciated.

The shock I would like to use is Blueshield Sani Shock 2 Calcium Hypochlorite 47.6

Ralph Davis

[chem geek]

You can use Cal-Hypo as your chlorine source to shock the pool if you'd like since your CH isn't too high, but keep in mind that for every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it will increase Calcium Hardness (CH) by 7 ppm. If your pool is clear and doesn't have algae, then you might have ammonia in the pool if it had zero FC at some point. Just keep adding chlorine and it will eventually hold. You can do a bucket test if you want to see how much chlorine that will take. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC.