High CH Due to Rock?

[momtaps]

Our CH level is always so high - and we have no signs of scaling. Our tap water has a CH of 170. Here are my testing results today:
FC 3
PH 7.8
TA 90
CYA 50
CH 770
We have a rock waterfall and 30' of weeping rock. The bottom of the rock is always submerged in the pool water. The builder called the rock "moss rock" but it looks like sandstone to me. Could the rock be high in calcium and it is leaching into the water? I can't figure out any other reason the calcium should be so high.
The water temperature averages 65 degrees.

 

[Melt In The Sun]

Nope, not from the rock. Your CH is high because your pool water evaporates and is refilled. So, one pool-full of water = 170 CH. Over a year or two, all that water evaporates and is replaced with new water...the CH does not evaporate, it stays. Now, you have 340 CH, 170 from the first fill and 170 from all the replacement water. Over time...it builds up. Eventually you'll have to dump and replace it. We have 200-ish CH in the water here, and after about 3 years it becomes unmanageable and I just dump it all and start anew.

 

[JasonLion]

The rock might well have some CH in it, and a little CH might be dissolving out of the rock, though I doubt it, but it wouldn't significantly affect the pools CH level. To raise CH by 600 you would have had to dissolve well over 100 lbs of rock, which would be very very obvious.

Your issue is caused by the CH in your fill water. As water evaporates, none of the CH evaporates. Then when you add more water to top off the pool you are raising the CH level. In especially arid climates the CH level can go over 1000 in just one season from evaporation. But even in more temperate climates the CH level will still climb noticeably each year when your fill water CH level is that high.