Total Hardness and Calcium Hardness

mfifield01

Well-known member
May 11, 2022
49
Austin, TX
Pool Size
16000
Surface
Plaster
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Liquid Chlorine
I noticed my CH was low last week (200). I added about 12lbs of Calcium Hardness increaser and it's sitting around 275 now. My wife was wondering why I needed to increase the water hardness, since everyone in our area complains about how hard the water is out of the tap. So I checked the tap water for CH and it's about 175 (no water softener at the house). It must be other minerals in the water that make it hard. Is there any concern about total hardness or other minerals getting high in the water? We tend to have a chalk or film on our tile above the waterline most of the time. The pool was first filled on 7/8. Below is the last test log.

FC: 5
pH: 7.6
TA: 90
CH: 275
CYA: 50
Temp: 82
CSI: -0.08
 

cledee

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Jun 23, 2020
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Concord, NH
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I noticed my CH was low last week (200). I added about 12lbs of Calcium Hardness increaser and it's sitting around 275 now. My wife was wondering why I needed to increase the water hardness, since everyone in our area complains about how hard the water is out of the tap. So I checked the tap water for CH and it's about 175 (no water softener at the house). It must be other minerals in the water that make it hard. Is there any concern about total hardness or other minerals getting high in the water? We tend to have a chalk or film on our tile above the waterline most of the time. The pool was first filled on 7/8. Below is the last test log.

FC: 5
pH: 7.6
TA: 90
CH: 275
CYA: 50
Temp: 82
CSI: -0.08
Typically if Hardness levels go above the recommended ranges, Calcium can start precipitating & scaling if your PH is high. You have a plaster pool and that requires calcium hardness otherwise if it gets too low, your water will start eating at the plaster to get it's Calcium.
 

mfifield01

Well-known member
May 11, 2022
49
Austin, TX
Pool Size
16000
Surface
Plaster
Chlorine
Liquid Chlorine
According to Taylor (link above) the Total Hardness doesn't matter, just the CH. I've got the CH in the manufacturers recommended range (200-400). I'll continue to check and keep it in that range.
 

JoyfulNoise

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May 23, 2015
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Tucson, AZ
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Unless your pool has a leak or you are exchanging pool water for fresh water by splash out, your CH levels will continue to climb as you refill the pool from evaporation. Therefore, you really don't need to add calcium in your neck of the woods. In very arid climates like mine, CH increases 200-300ppm per year simply due to evaporation and refill. This is why I installed a whole house water softener with a line run outside to my pool autofill. Now my CH stays constant.

You will need to monitor your CH levels regularly (monthly is a good place to start) and then adjust them accordingly. If you live in an area where the municipal supplier places restrictions on water use for pools or irrigation, then you may want to consider going the softener route. There are portable RV water softeners available that can be used to do top-offs but, if you want something more akin to your autofill, then you'll need to consider a whole-house unit.
 
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duraleigh

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Tiniest of hijacks......

In our 15+ years as a forum, we have had reported many, many instances of calcium saturation.......most commonly scale.

I can only recall perhaps a handful of instances where the water was "aggressive" and leached calcium from the pool

Common sense tells me those instances should be roughly equal to but they are not.......not even close. I don't understand why that is.

Should the range be lowered? say 0.0 to -5 ?

I am above my pay grade on the chemistry so perhaps I am overlooking an obvious answer??
 

mfifield01

Well-known member
May 11, 2022
49
Austin, TX
Pool Size
16000
Surface
Plaster
Chlorine
Liquid Chlorine
Unless your pool has a leak or you are exchanging pool water for fresh water by splash out, your CH levels will continue to climb as you refill the pool from evaporation. Therefore, you really don't need to add calcium in your neck of the woods. In very arid climates like mine, CH increases 200-300ppm per year simply due to evaporation and refill. This is why I installed a whole house water softener with a line run outside to my pool autofill. Now my CH stays constant.

You will need to monitor your CH levels regularly (monthly is a good place to start) and then adjust them accordingly. If you live in an area where the municipal supplier places restrictions on water use for pools or irrigation, then you may want to consider going the softener route. There are portable RV water softeners available that can be used to do top-offs but, if you want something more akin to your autofill, then you'll need to consider a whole-house unit.
Thanks for the advice. My initial concern was seeing it at 200. Pool Math recommends 250+ and NPT recommends 200+. I'll leave it alone and check monthly.
 

ajw22

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Jul 21, 2013
38,807
Northern NJ
Pool Size
35000
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Plaster
Chlorine
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Pentair Intellichlor IC-60
Tiniest of hijacks......

In our 15+ years as a forum, we have had reported many, many instances of calcium saturation.......most commonly scale.

I can only recall perhaps a handful of instances where the water was "aggressive" and leached calcium from the pool

Common sense tells me those instances should be roughly equal to but they are not.......not even close. I don't understand why that is.

Should the range be lowered? say 0.0 to -5 ?

I am above my pay grade on the chemistry so perhaps I am overlooking an obvious answer??

I think that question is in @onBalance pay grade.
 

onBalance

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In The Industry
Jul 25, 2011
1,325
Utah
Imo, the current and established range for the CSI and LSI should remain the same because that provides good protection for all concerns and situations.

I believe the reason that scale is more prevalent and common than etching is simply because most tap water sources in the country contain high calcium levels. So that lends itself to scaling issues as opposed to etching. Minor scaling is also much easier to detect than minor etching, which can lead to false conclusions. There are areas where the calcium and alkalinity levels of tap water are very low, and that lends to results of etching over time. I am very familiar of those situations.

It is not a good idea to suggest constantly maintaining negative CSI or LSI numbers simply because doing so will indeed begin to etch pool plaster and increase wear and tear on plaster. The current recommended ranges are appropriate.
 
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