Calcium Hardness decreasing

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,667
Tucson, AZ
Yup. Mannitol powder and BTB indicator is what you need. I typically use a 50mL beaker (sits on the SpeedStir just fine) so I can get the 4ppm/drop accuracy. I use the test several times per season.
 
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MyAZPool

Gold Supporter
Jul 3, 2018
964
Arizona
So here’s the deal as to why I asked. In arid climates we tend to play a game with our fill water and pool water where we just let the CH do whatever it wants and then adjust TA and pH to get the CSI where we want. The problem is, when the TA of your fill water is far away from the TA of the pool water, then that adds to the upward pressure on pH rise since you’re always fighting to keep your TA lower than what it naturally wants to be.

So I would say that your “optimal” CH target is one that allows your TA and pH to be as close to your fill water TA and pH. At a CH of 250, you can easily let your TA rise to 100ppm (closer to your natural fill water) and let your pH live between 7.6-7.8, and your CSI will be fine. Then, because you are adding water to your pool that’s chemically very similar to the pool water, the pH should need less adjusting with acid as long as you keep your sources of aeration minimal (aside from letting swimmers have fun).
Matt,
Quick question. After some rains, it was a good time to do a backwash since the filter was due and I had the extra water at the time.
Full test today and the CH dropped 25 ppm so that's good. But the TA also fell from 70 to 60. Reading your post above I kind of got the impression that the TA would rise a bit as the CH dropped. But it didn't. So should add in a little baking soda (about 3lbs according to pool math) and at least kick the TA back up to 70 (where it normally lives). I was kind of shocked to see that TA drop because normally it always hovers around 70.
Thanks...
r..
BTW. Based on our discussions regarding Boric Acid, since I just did the backwash, so I figure now would be a good time to kick up the borates to 70ppm. That will take me about 30lbs of boric acid. :)
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,667
Tucson, AZ
Your TA results are a bit weird. But I just looked back at your thread with the test results on your city versus softener water and I see your city water at 110ppm and your softener at 90ppm. The two numbers should be the same as a water softener only removes calcium and has no effect on TA. There are ion exchange resins that can remove anions like carbonate and bicarbonate but those are super-specialized and not typically found in any residential application. My guess is your TA testing is a little wonky. I really wouldn't add any bicarbonate, your TA will rise naturally. It's just going to take longer.

For reference, rain water is naturally low in TA, about 20-30ppm from absorbing CO2 in the atmosphere and other junk. But I doubt you got enough rainwater to really effect TA.
 
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MyAZPool

Gold Supporter
Jul 3, 2018
964
Arizona
Your TA results are a bit weird. But I just looked back at your thread with the test results on your city versus softener water and I see your city water at 110ppm and your softener at 90ppm. The two numbers should be the same as a water softener only removes calcium and has no effect on TA. There are ion exchange resins that can remove anions like carbonate and bicarbonate but those are super-specialized and not typically found in any residential application. My guess is your TA testing is a little wonky. I really wouldn't add any bicarbonate, your TA will rise naturally. It's just going to take longer.

For reference, rain water is naturally low in TA, about 20-30ppm from absorbing CO2 in the atmosphere and other junk. But I doubt you got enough rainwater to really effect TA.
Matt,
Thanks very much for the info. Yea, about the discrepancy re the TA between the City and and softened, Marty got me squared away with that. I just "dummied" up the first test. TA on both are 110.

Since, I'm still barely in the 60 to 80 range anyway. I'll cancel the proposed baking soda idea and just let the 110ppm TA fill water do it's job and so it (baking soda) doesn't mess with the pH.
Thanks much for keeping me on track. I appreciate the help!
All the best...
r..
 

MyAZPool

Gold Supporter
Jul 3, 2018
964
Arizona
Do you have an acid dosing tank?
Matt,
Yea, sorry. The dinner bell rang.
Sure. Using the IntellipH. When I did my full test yesterday, the pH did tick up .1 to 7.8 (normally it lives at 7.7), but I just kicked up the MA dosing from 65% to 70%. That'll take care of that. I'll test in a day or two and probably have to adjust it back down to 65%.
r.
 
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