New plaster - calcium levels at startup

[trivetman]

I just got my welcome packet in preparation for a pool renno in the spring - including replastering.

Startup instructions say to maintain a calcium level of 125-175 ppm for the first 14 days. After 14 days levels should be higher (225-375 ppm).

I am curious why they want it so low for the first two weeks. Anybody know?

 

[JamesW]

New plaster creates "plaster dust", which is calcium hydroxide that becomes calcium carbonate.

This can scale a pool in short order if the pool is not brushed and the pH kept under control.

Typically, maintaining the CSI between -0.3 to 0.0 will control the scaling risk.

 

[trivetman]

So the plaster dust will raise the CH level in the first two weeks. Putting initial CH level at the usual 250-300 level is too high considering the level will rise from that point due to the dust?

 

[JamesW]

The dust can scale if the CSI gets too high.

Raising the calcium level raises the CSI and increases the risk of scaling.

Brush daily and maintain the CSI between -0.3 and 0.0 and you should be good.

What are your readings for pH, TA and calcium hardness from the tap?

 

[trivetman]

What are your readings for pH, TA and calcium hardness from the tap?

dont know but Ill be trucking in water for the fill so tap water measures aren’t that important.

 

[JamesW]

Ok, calcium levels will increase some from plaster dust.

Brush daily and maintain the CSI between -0.3 and 0.0.

 

[trivetman]

I am glad you brought up the CSI. The full set of guidelines for the first two weeks are

FC: 1
Ph: 7.0 - 7.2
TA: 60 - 80
CH: 125 - 175
CYA: 0 - 30

With these numbers the absolute highest the CSI will be is -0.75 and it will likely be lower as the water will be cold in the spring.

After two weeks the guidelines for everything are back to more normal ranges.

So why so low on the PH and TA? My initial thought is the PB is so worried about scaling at startup their chemistry guidelines are geared to avoid it at all costs. Are there long term problems I might have from following these guidelines at startup?

 

[JamesW]

Those numbers are too low, in my opinion.

If the contractor is using a brand of plaster, there should be written startup instructions.

What exact plaster will you get?

 

[trivetman]

Basic white plaster. PB had brand names on the quartz and pebble upgrades but i dont have the manufacturer of the white plaster we are getting

 

[JamesW]

My opinion is to do a balanced startup.

The contractor is the one responsible for the warranty, so you want to try to make sure that they are ok with whatever startup method you choose.

Maybe ask them if they are ok with a more balanced startup or if they have a reason that they prefer to have the water more aggressive.

 

[trivetman]

Makes sense - thanks