What is the importance of CH on new plaster?

[susa]

There are slight variations on Calcium Hardness targets, as reported here and here and here

TFP Water Chemistry:

A plaster pool should have CH levels between 250 and 350 if possible.

TFP SWCG Guidelines:

Adjust Calcium Hardness to 300 ppm for plaster

From Diamond Brite Install Ref:

Calcium Hardness: 200 PPM

From Pentair IC40 Manual:

Calcium Hardness 150 to 400 PPM

Since my pool is on day 25/26 and am planning on starting to add salt in another 30 days, what should be the ideal CH level? What should it be while the plaster is curing?

 

[benavidescj]

The ideal CH level will depend on current water chemistry and your location in the country. The goal is to maintain balanced water chemistry so that the plaster will not either suffer the corrosive effects of the water (seeking calcium) or the opposite (calcium build up on surface in the form of scale). The pool calculator is your friend when trying to determine the correct calcium level for your particular case. When you plug in your values in the pool calculator you want to maintain a Calcite Saturation Index (CSI) between -0.6 and +0.6. Too negative and the pool will tend to draw calcium from the plaster. Too positive and the opposite happens, calcium deposited on the surface in the form of scale.

You may live in a part of the country where calcium is present in the water supply in high concentration to start with. So every time you add water you are adding calcium. And with nowhere to go the calcium will build up quickly. Now this is not necessarily a bad thing. Some people live with calcium levels at or above 600 but you have to be careful not to let the pH rise to far above 8.0 or you will start to get scale.

All this said, in a new pool you will get high levels of calcium build up over the first few months to over a year due to the curing process releasing calcium. So you may need to release some from time to time by partial drain and fill, again, if your water is not real high in calcium. Other alternatives to remove this calcium is by reverse osmosis, if it is available in your area. I have a CH level of 520 as I am living with a new pool right now as well. I am careful to watch my pH closely and have not had an issue with scale.

Bottom line, use the pool calculator and try to maintain a reasonable CH level. If you CH gets too far away from the recommendations, say 150 or over 500 you need to be cautious with your other levels such as pH and TA.

 

[susa]

I maintain PH at 7.0 for the first 30 days (recommendation from diamond brite crew), then at 7.4 for the next 30 days.

My initial question is really, what should it be for "new plaster" as you can see from the 4 sources I quoted and linked, the recommendations are not uniform.

am located in the deep south (6 hours south from Fleming Island) and we *never* add water to the pool as it's always replenished naturally.

when the diamond brite was done (25/26 days ago) the water from a very clean municipal supply was further cleaned by being filtered through a massive (5 ft tall scuba tank looking device) filtration system specifically made for pool refills. it came out very blue and absolutely void of chemicals and metals.

In case it matters, Pump is running 24/7 and has been on around the clock since refill. It costs hardly anything to run the VF @ 99watts

 

[duraleigh]

Generally, the forum suggests a wide range of CH as acceptable....varying from 200 to 400. I know it can be higher with good water m,management and suspect it could be a little lower as well.

I'd target 300 in a plaster (on start up, too) and not worry about the variations from that number.

 

[Guest]

NPC (National Plasterers Council) recommends 200-400 ppm CH for swimming pool plaster, which is generally accepted by all plasterers and pool builders. I'd get/keep it at 300 ppm like Dave (duraleigh) suggests, as you should have no argument down the line for being firmly in the middle of those guidelines.

 

[susa]

ok, will do.

Is there some anecdotal evidence or information that would tell me, how does a new diamond brite pool behave upon initial fillup with ultra-filtered water ? for example, with PH, we all know it tends to raise PH to alkaline and it's a slow daily addition of a cup or two of muriatic acid.

Is there a similar normal (CH up/down) tendency, assuming no fillup water other than rain, while the plaster cures ?

 

[Guest]

Since all pools behave differently, I would just keep an eye on it (like it sounds like you have been) and get your CH in the middle. CH does not go away, so once you have it there it should stay put! It can't be controlled with chemicals like most other pool chemistry levels.

 

[TFP_wanna_be]

I'm sitting at 170 about 8 days after the resurface... I'd rather be 200+... I'm sure I'll get it dialed in...