Very high CH - What causes it to rise?

[phalcon51]

I had my pool replastered in Sept. 2010 and I've kept a pretty close eye on the chemistry, but the CH level has been steadily climbing. My fill water has a CH of 140 and as of Feb. 2011 the pool CH was 250. Since then it's been steadily climbing until it's now up to 575. I'm going to have to drain and replace over half the water in the pool, or about 15,000 gal., to correct it. Can anyone tell me why it has climbed so high and what I can do to prevent this from happening in the future?

Here's my current chem levels if it helps

FC - 3.5 Range - 3 - 5
pH - 7.6 Range - 7.4 - 7.8
TA - 70
CH - 575
CYA - 60
Salt - 4060

Thanks for any help

Gary

 

[JasonLion]

When water evaporates, only the water evaporate. It doesn't take any of the chemicals along with it. Then, when you top off the pool with additional water, the additional water comes with more calcium. At that point you have the CH that was already there, plus new calcium from the top off water. Because of this, CH will constantly rise. Eventually you will either need to replace most of your water or get a reverse osmosis treatment.

 

[257WbyMag]

Have you checked your fill water CH?