What is considered normal CH while new Diamond Brite curing?

[susa]

CH=Calcium Hardness

Testing range is usually listed as 150-500 ppm

I used municipal water, ultra-filtered (paid separate filtering service company and tested water as mineral free) when filling up pool initially and had CH steady around 200 ppm month one and two (60 days later).

Without having added anything except liquids and CYA, it appears CH is slowly climbing, today at 250.

Is that to be expected while DB is curing?

Tests on 31.12.2010
FAC 5
TAC 5
CH 200
CYA 50
TA 120
pH 7.4

Tests on 17.1.2011
FAC 5
TAC 5
CH 250
CYA 60
TA 80
pH 7.4

 

[JasonLion]

Yes. As plaster cures it raises the PH and also adds both TA and CH to the water. Adding acid to keep the PH under control usually lowers the TA back down, but the CH increase stays around until/unless you replace water. This effect is not as dramatic with Diamond Brite as it would be with plain plaster, but you will still see it happen some. Normally the effect is largest during the first three to four weeks after the surface is applied, and then slows down significantly, continuing at a slower rate for up to a year.

It is also possible for the CH level to go up if the PH gets below about 6.8. Low PH will leach CH out of the pool surface. The lower the PH gets, the more dramatic this effect will be. If the PH gets too low for too long there will be visible damage to the surface.

It is also possible that a change from 200 to 250 could be testing error. This is quite likely if you are using test strips or a pool store for testing, much less common though not out of the question if you are using something like the TF100 or Taylor K-2006 for testing.