Source of Calcium

[tmarcoux]

I am posting this on behalf of a friend who just purchased a house down the road which came with a pool. I have tested the water several times, and everything appears to be close, except for the calcium (CH=700). Using Poolmath, he will have to replace 2/3 of his pool water with municipal water to get it to 350. Here's my question: what are the various sources of CH? I only know of two sources: fill water (150 in my area) & PS Pool shock. We have the same water source, and I tested both his pool and tap water.

I have told him that a partial drain/fill is needed, but I'd like to isolate the source so he's not doing it more than once.

Here's the specs on the pool/tests. Please ignore the information in my sig.

Pool
10,000 gallons
Plaster
SWG
DE

FC=10
CC=0
pH=7.7
CYA=80
TA=80
CH=700+
Salt=3,500

 

[JasonLion]

The CH almost certainly came from the fill water. As water evaporates, the CH stays in the pool. Then when you add water to top off the pool you are adding more CH. Over time the CH level goes up.