yellow spots in pool

[cbrown9079@yahoo.com]

I have a 13,000 pool a year old and Ph and clorine have always been great. I am now having big yellow spots in the pool and hot tub which I can brush away but they keep coming back. Just had my water tested and it showed no clorine. What can I do? I have clorine tablets and they seem to be disolving?

[pool whisperer]

Have your water tested for stabilizer which keeps the U.V. light from burning off your chlorine. And give your pool a good shocking of liquid chlorine.