What is causing Calcium hardness to go up so fast?

[march2012]

Austin tx city water

New plaster
5/1/2012 measured fill water at 175 CH
5/15/2012 160
5/30/2012 250
6/10/2012 410
9/2/2012 620
4/24/2013 500

1) had a skimmer leak so turned over some water (not sure how much).
2) have a cartridge filter so dont backwash
3) pool guys lowered the level about 2 ft (out of 5ft) to fix some issues around march of 2013.
4) use bleach only

During the last 12 months my CYA went to close to zero twice.

Im just trying to understand what is happening. Did the calcium go up due to the new plaster plus some from evaporation and refilling? Then we lost some when the lowered the water level. During the same time Ive had to add more CYA twice (essentially went to zero).

1) What is possibly going on with CH?
2) Why did CYA go to zero twice?


No algae problems ever.

 

[JasonLion]

Where do you live? In some areas very high fill water CH levels can cause problems. Check your fill water CH levels. High fill water CH levels can make CH levels go up quickly. CH doesn't evaporate, so every time you top off the pool you are adding more calcium. In most of the country this is not an issue, but when it is it can be a very large issue.