Combined Chlorine =1.5, how long...?

[Pmchick]

Hello,
An indoor pool had a combined chlorine reading of 1.5. The pool is 11,730 gallons. I added 1 gallon & 1qt of liquid chlorine(12.5%) to it, to bring the level up to 15ppm. The FC before shock was 1.5ppm.
Well, about 15min after adding the bleach, I tested the water and the FC was only 11ppm(I tested the water in several spots). I added in another gallon of chlorine. Waited about 20min and the FC level was than 16.5, but, when I tested for Combined CHlorine, the reading was 1.0....
How long does it take to eliminate all of the combined chlorine? The ventilation is AWFUL in this pool and there are no windows and air exchange is poor.
I am using the Taylor FAS-DPD test kit. THere is no visible algae in this pool and water temperature is maintained at 90 degrees, as it is a therapy pool.

Thank you for yourhelp,

 

[JasonLion]

In an indoor pool with bad ventilation it can take a really long time for CC to come down. Ventilation is very important and helps a great deal, both to clear CC and in general. You can also try MPS, non-chlorine shock, which is better at eliminating CC than chlorine is in indoor pools. The one thing to watch out for is that MPS will test as CC, so if you use it regularly it is worth getting the special reagent to prevent it from reading as CC in the test.

 

[Pmchick]

THank you, Jason. The pool has been sitting untouched since Friday, (I am not there nor is anyone else to check out the levels). I'm hoping that 3 days was enough to get rid of the chloramines, I guess I will find out tomorrow.

Also, when using the FAS-DPD kit, should I be filing the sample tube to 25mL or is 10mL suffiient? Does it make a difference as long as I multiply the numbers appropriately with either .2(25mL) or .5(10mL)?
Thank you again for your help.

 

[JamesW]

Also, when using the FAS-DPD kit, should I be filing the sample tube to 25mL or is 10mL suffiient? Does it make a difference as long as I multiply the numbers appropriately with either .2(25mL) or .5(10mL)?

The 10 ml is usually sufficient.

 

[257WbyMag]

Using the 10 ml sample will save you money because you won't use as much testing reagent as you would with the 25 ml sample. Besides, 0.5 ppm accuracy is just fine for pool purposes.