Perfect Pool Problems???

[KPalom]

I have a 13600 gallon pool. I recently had algae and shocked my pool to clean it. Everything read fine and the chlorine levels were perfect. A day later my pool read 0 for Free Chlorine. I have taken my water to be tested and everything reads perfect. I was told to shock it again, so I did and it read to much chlorine. The next day it read no chlorine again. I have changed how long I have run my pump to all day, I have put more chlorine tablets in, I have shocked again and again and the same thing happens after I do that. What could be wrong? Please Help??

Free Chlorine 0
Total Available Chlorine 0
CYA 80
Total Alkalinity 80
pH 7.8

[PoolDoc]

Get a cheap OTO test kit, and test with that.

I'm not sure how you are testing, but if it's with DPD tablets, you may be reading 0 when it's really 15 ppm. OTO isn't especially accurate, but it will give you a reliable indication of what's really there.

Ben

[KPalom]

I was testing with a cheap kit and now I have a Taylor K-2005?

[Watermom]

What are you using to shock with, meaning ingredients? What kind of pool do you have and what type of filter and size of pump?

[KPalom]

The pool is in ground pool, DE Filter, Pentair variable speed pump, Chlor Brite is the product I am using to shock. I started out one week using 2 pounds to shock when I had algae. Then when I saw no chlorine and checked everything and had the water tested fine, they said shock again so I used a pound, then it did the same again so I used another pound.

[madwil]

your CYA is 80, so I would not use the chlorine tablets anymore; most of them I think are trichlor, which will continue to raise your CYA and cause you to have to maintain higher FC levels!
the 2005 kit is DPD, not DPD-FAS, and as Ben stated it can bleach out at higher FC levels- indicating 0 when really 15! The OTO kit will turn orange or brown at higher levels, instead of clear, so will give you
true, if not accurate, indication of FC presence!