I'm unable to keep any amount of chlorine in my pool, total or free. Even after shocking in the evening to 20ppm after the sun was no longer on the pool, the level dropped back to zero within a couple hours.
The water has been tested by two different pool testing places and everything is in range except for chlorine. Also, CYA dropped from 31ppm to 8ppm in one day?
(The first test done by our local ACE Hardware store read 31 and the second the next day by a pool store read 8. My test strips actually concurred with both tests.) This problem actually started last summer with an intense heat buildup and I have yet to get it under control even after shocking many times. Pool temp is 82F.
The liner was replaced in 2004 and the pool water has not been changed since except of course rain and to add water due to evaporation. Should I drain the pool and start over? Not concerned about structure with draining. It's been done before and designed to stand empty.
Thanks for the question Gary
My first question would be are you testing with strips or a Taylor FAS-DPD K-2006 test kit. It's this kit that you should be using.
Next, you should shock at night and take another reading in the morning after the filter been able to run for the entire night. Does the shock hold until morning? If it does hold but the chlorine is dissipating through the day, you probably don't have enough CYA/stabilizer in the pool water. It should be between 30 - 50ppm.
It may take a few days to a week for CYA to show up in the pool if it's being added every or every other day. Use Dichlor shock and Trichlor tabs to keep the CYA in check. If you chlorine reading is showing nothing, there may be a chance that the chlorine is so high that it's actually bleaching out.
This happened to one of the guards
at the YMCA. There was an accident in the hot tub, (puke I think), so she put alot of chlorine in to take care of the problem. She tested the chlorine after 30 minutes and there was no reading. She called me and I went down to the Y and tested it myself. Sure enough, it registered zero.
So here's what I did and what you can do. Take the vial (with the FAS-DPD kit) and fill it up to the 25ml mark with pool water, then fill the rest of the way, up to the 44ml mark, with tap water. What you just did is dilute the chlorine level. Mix it up a little. Then pour out to the 25ml mark. Run your test as usual.
When you get a reading, simply double it and you'll have your chlorine reading. This will tell you if you have bleached out the first reading. If you don't have an FAS-DPD kit, you can dilute a sample and take that into your local pool store for analysis. It might be that your chlorine demand was caused by something that got into your water. Ammonia from bacteria may cause a higher than normal chlorine demand.
CYA can be used up by anerobic bacteria in a closed pool. The bacteria will excrete ammonia compounds in the pool. If the bacteria is the problem, you'll need to basically shock and keep the chlorine level to about 15ppm all day long until the chlorine holds.
It may take lots of chlorine to do this and the expense will probably add up pretty quickly. If you keep shocking and have the CYA in line, and all of the other chemical readings are in line, as a last resort, I would advise you to drain at minimum 1/2 of the water and restart.
The bacteria producing ammonia would be my best guess. By the way, the guard who put the chlorine in the hot tub got the chlorine reading up to 80ppm. Hope this helps and good luck with your pool.