Calcium Hardness keeps rising

[macscom5]

My pool's calcium Hardness keeps rising and I can't figure out why.

Today's test
FC- 3.5
CC - 0
PH - 7.5
TA - 80
CH - 450-475
CYA - 80

On 9/25 CH was 270. On 10/11 CH was 390.

I'm using the TF-100 kit and tested CH twice today with readings of 450 and 475.

I have an auto-fill, but the tap water CH is only 125.

Any ideas? Thanks, Scott

 

[polyvue]

Do you use a pool service? How do you shock the pool? How often in the past two months has it been shocked? I'm wondering whether you or someone else has been adding Calcium Hypochlorite in the form of shock powder or pucks, or possibly dumping Calcium Chloride in the water when you're not around. Whatever the source, you may want to think about doing a partial drain and fill (say 10-20%) to reduce it, especially if it continues to climb.

 

[macscom5]

I do all the work myself. I last shocked at the end of August. The only thing I have added in the last two months is MA (regularly), about 3 Lbs of baking soda, and about 4 lbs of CYA (99%). No one has been swimming much in the last month.

I understand about draining/refilling, but I really want to figure out what is causing the rise so I don't have to keep dumping water.

 

[duraleigh]

To my knowledge, the only way you can increase CH in a pool is thru fill water (which you're not) or by adding it with the chemicals polyvue has mentioned (which you're not).

I have no explanation.

 

[PaulR]

How old is the pool? Was it recently resurfaced?

 

[joshreis]

Evaporation only takes up pure water, leaving the calcium that was in the pool behind. When you go to refill your pool to the proper water level, the 125 ppm of CH thats in the tap water is going into the pool. Its also possible, but unlikely, that the water is taking the CH out of the plaster itself.

 

[duraleigh]

OP's posts indicate pool is not new.....but doesn't confirm that.

For the amount of increase indicated, evaporation would have to be enormous.....in Sep and Oct......that doesn't seem likely.

Unless this pool was put in late Summer, I am still at a loss.

 

[PaulR]

The other possibility, much as I don't like to suggest it, is testing error.
--paulr

 

[macscom5]

Pool was completed in June. I went to a local pool store that has been relatively good in the past and they measured CH at 320.

Looks like I'm going to have to partial drain for other reasons as well so I will try that and continue to monitor.

Thanks, Scott