Why did Cal increase?

Butterfly

TFP Expert
LifeTime Supporter
May 31, 2007
10,045
South Carolina
#1
Today's #'s

FC......6.5
CC.....0
TC.....6.5
pH.....7.7
Alk....110
Cal....300
CYA...30 - 40
Temp...82 (water has not been this cool since May 1st)

Not concerned w/the pH & alk....... added MA to knock it down. New-ish plaster :evil:

My questions is: Why did my Cal go from a steady 250 to 300? Have added nothing except the normal bleach and the MA. :?: I did the Cal test twice. I am not complaining about the cal of 300, in fact, I'd prefer it to be there; however, I was laying low to see if it would creep up on its own because of the new plaster??? Could this be the cause? :?

Joyce
 

JasonLion

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May 7, 2007
37,879
Silver Spring, MD
#2
New plaster will raise the CH level of the water as it cures. This happens quickly for the first three or four weeks and then much more slowly for up to a year. TA and PH also rise as the paster cures.
 

Butterfly

TFP Expert
LifeTime Supporter
May 31, 2007
10,045
South Carolina
#3
Thanks, Jason. The CH was 200 - 210 for Mar, Apr & May. In June, I increased it to 250 and it tested at 250 until today. It seems really curious that it would jump to 300 on its own. Does that seem like a reasonable jump for the plaster curing process?

Also, I am still using Ben's kit from last year and maybe I shake it up a little better 'cause there is less to shake up! :roll: I'll check it again next week and see what its doing. Have a great weekend.

Joyce
 

JasonLion

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May 7, 2007
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Silver Spring, MD
#4
Curing happens more quickly when the water and plaster are warm, so it is not out of the question that it was rising very slowly in the spring and then rose more quickly in the summer, but it wouldn't have jumped suddenly just from plaster curing.

The thing that can cause sudden jumps is if your calcite saturation index gets very negative. That can pull calcium out of the paster quite quickly. Right now you CSI is a little towards the scaling side (nothing to worry about), nowhere near pulling calcium out of the plaster. But if your PH was way lower (noticably below 7.0) at some point that could have done it.

Other than that, you would have needed to add some cal-hypo or calcium chloride, or fill water that was high in calcium. Or your test kit is getting old and isn't working correctly any more.
 

chem geek

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Mar 28, 2007
12,082
San Rafael, CA USA
#5
The other source or calcium is in the fill water. If you had lots of evaporation, then the fill water would incrementally add whatever calcium it has to the pool water. This is in contrast to dilution from splash-out or backwash that would reduce the CH unless the CH in the fill water is higher than the CH concentration in the pool.

I had my pool's TA level rise from 110 to 140 (measured at comparable pH) and was likely due to evaporation and refill with water that has around 80 ppm TA over many months (one season).
 

JCJR

LifeTime Supporter
May 4, 2007
267
Miami
#6
Joyce,
My CH did the same thing. I had new plaster since April and my CH was 260 for 4 months, I think I had scale because my plaster had spots and looked white ( my ph crept to 8.0 a couple of times) so for the last 2 weeks I have lowered my PH to 7.2 and brushed with a combo (s/s with viynl) brush and I was picking up dust like most people report after a new plaster job. My pump was not installed until 3or4 days after my plaster was done and I think that is why I had so much trouble with scale. After 4 days of low ph and brushing I no longer have dust coming from my plaster, I did test my CH and it is now at 430. It jumped 170ppm in 3 weeks time. I tested twice and that is what I got. I'm sure CH was 260 because I must have tested it maybe 10 times and that is what I always got. I hope it stops creeping up because I don't want to partial drain/refill.