High CYA - Do I need to drain pool?

[olaggie]

We use a pool company to provide weekly service -- cleaning and maintaining chemicals. We were informed yesterday that our CYA is high (150ppm) and that we should completely drain the pool ($330 just to drain). They also advised that some customers also hire another company to power wash the drained pool to ensure the plaster does not retain CYA. Even then, they say they feel confident the CYA will be back to normal but make no guarantees.

In researching causes of CYA, I keep seeing that overuse of certain types of chlorine is the main contributor. How do I know if the company is overusing chlorine? For example, over the past couple of months, our chlorine reading has been >5, yet the company continues to add chlorine tablets on a weekly basis. They've also been adding tablets and shocking the pool every week for at least the past 4 weeks despite the chlorine level being >5.

I guess I'm wanting to know if 1) draining the pool is an extreme measure or typical in these situations, 2) will draining the pool typically fix the problem, 3) is it normal to continue adding chlorine tabs when the chlorine level is >5.

Any guidance is appreciated. I hired the pool company to not have to worry about such things so I'm a little concerned, based on my admittedly limited research, that the overuse of tabs has created the problem. I am also aware that I don't know much about this area. I suppose what I'm really looking for is confirmation that the pool company is on the right track.

Thanks!

[Denniswiseman]

Chlorine gets used up, you don't just add leave and forget, it has to be maintained
Excessive CYA renders your chlorine ineffective and you have to use more to get the same sanitation
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm
Continuing use will raise your CYA
On checking the Chlorine / CYA Chart anything is acceptable between 30-60
So to get to 50 you would need to drain 2/3 of the pool water and refill

Use these common products to balance your pool
Liquid chlorine (sodium hypochlorite or plain bleach)
Muriatic acid (hydrochloric acid) to lower pH and TA
Bicarbonate of soda to raise TA
Aeration will raise pH only
Soda ash will raise pH and TA

You really need to get yourself a decent FAS/DPD test kit (Taylor K2006c or TF Testkits TF100 in the states) to get accurate results as maintaining an appropiate shock level means testing quite often during the day
There is a difference between total chlorine and free chlorine which is combined chlorine (the used up chlorine)

The pool company is ripping you off with a full drain and acid wash. Tabs are simple to use
Hope this helps