# Thread: Hard water calcium scale question

1. ## Hard water calcium scale question

OK as you can see in my sig we battle scale build up constantly here with our city water on everything from faucets to showerheads etc. However when I do a calcium hardness test with tf-100 I test a low 125 such that I need to add something [calcium chloride] to bring it up. I'm confused can someone shed some light on this?
Thanks!

2. ## Re: Hard water calcium scale question

CH is not the only factor for determining scale potential. Enter all your test results in PoolMath and it will give you a CSI number. Keep that number between -0.3 and 0 to avoid scale in your pool. More here, Pool School - Calcium Scaling

3. ## Re: Hard water calcium scale question

Right but I'm still only testing 150 ch for the municipal water in our house yet we still have massive scale calcium build up.. i still have yet to hear a good explanation regarding this...
Incidentally my csi is -.13

4. ## Re: Hard water calcium scale question

Also remember that even if your fill water is only 150, CH never leaves the pool unless you exchange that water. So basically the CH in the pool keeps building higher & higher with new refills following evaporation. Your CH may be 200 in May, then grow to 250 or more by June or July depending upon how much more water was added. The only way CH itself will drop is if you drain water and replace it with "soft" water. So to compensate for the CH growing, we make sure to never let pH and/or TA get too high to keep the CSI balanced.

5. ## Re: Hard water calcium scale question

OK thanks that's good to know so with my csi at -.13 I will leave it as it will increase over time. But i still dont understand how we battle calcium scale build up in the house on faucets etc when our water is only ch 150?

6. ## Re: Hard water calcium scale question

Because CH is not the only factor in determining scale potential. It is a combination of alkalinity, pH and CH. In the right combination CH at 150 can also leave scale. Just like it is possible for pools with CH at 1200 not to have scale with the right pH and TA. It is all about the scale potential of all of the measurements.

Test your tap water and figure out what the CSI is.

7. ## Re: Hard water calcium scale question

Ah OK I get it. I just assumed due to all scale build up on faucets tap water would test high on a ch test. This forum is teaching plenty. Thanks!

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