Climbing CH

[Pudge]

Hello all,

The CH in my 11 month old plaster pool continues to climb and has now tripped 500 from approximately 250 ten months ago. The pool surface is smooth to the touch and has no signs of scaling, but I don't know what is causing the rapid rise in CH.

Fill water has a CH of 110.

I've been monitoring it since I took over pool duties last September (August build) and have been every careful (read OCD) about the chemicals and water additions. To help manage the growing CH, I've been vigilant to try to refill as much as possible through rainwater by backflushing before anticipated rainfall. (Living in Louisiana gives us ample rainfall opportunities.)

In addition, being a bit OCD, I backflush often, after about 25% bump in clean pressure. (Clean pressure of 11, backwash at 13-14.)

At that time (last September) the CYA was about 60. Through a series of backwashings, rainwater refills, etc, the CYA actually got down to 35. (Is now back to 40 through a little bit of puck use.) With nearly half of the CYA removed, I would tend to believe that nearly half of the CH had been removed as well.

The pool does have a PH rise issue, but is easily managed by MA. I tend to keep the PH at 7.7, but have brought it down to as low as 7.2 on occasions.

Not that the FC matters, but it has NEVER fallen below 3 and I usually am able to maintain an FC between 5-8. Have never tested positive for CC.

With the exception of 9 pucks, the only method of chlorination since September has been Chlorox Regular bleach 8.25% or Walmart's Great Value bleach 8.25%. Have never used Cal-Hypo.

Here are this mornings results taken with a TF100 (with Speed Stir):

FC 5.5
CC 0
CYA 40
TA 60
PH 7.6
CH 510
Borates 35
Water temp 84

One last piece of the clue - I run the Polaris 280 a lot. Greater than 3 hrs per day on average - sometimes as much as 6 hours. Could this be causing plaster erosion, getting calcium in the water?

Sorry it's not as exciting as a green pool without a test kit, but does anyone have a clue on how I can better manage the CH? :-D

Thanks for a great resource - Pudge.

 

[BoDarville]

Pudge,
Welcome to TFP

What you are experiencing is common. In a new plaster pool or refinish, the CH will rise more quickly. The rise due to that should begin to level off though. On an ongoing basis, CH tends to drift up over time due to water evaporation - water evaporates whereas calcium does not. Every time you top-off the pool with tap water, calcium is being added. As you have correctly surmised, rainwater is the ideal fill water as it has no calcium so anything you can do to utilize rainwater would help.

To guard against scaling, pay particular attention to managing pH. Given the current water temps, you may want to lower your pH to around 7.4. You want to keep CSI slightly negative.

BTW, here is a great thread on managing scale: Progress on Scale

 

[JasonLion]

With high fill water CH levels your CH levels are going to rise no matter what you do. You want to continue using rain water to slow that down as much as you can, but unless you have a water softener, all that will do is slow the rise down. As CH goes up you want to lower PH and TA to compensate, least you risk calcium scaling. Eventually you will get to a point where CH levels are too high, at which point you either need to replace most of your water or see if reverse osmosis treatments are available in your area.

 

[Pudge]

Thanks - I guess I'll just have to be more agressive with water replacement. Appreciate the help!