Some pool math help needed

[crusemm]

OK, so in the efforts to simplify my life, especially pool maintenance, I recently installed a SWCG. In order to get as much life out of it as possible, I know I have to keep my water balanced. My primary issue is pH. My fill water has an extremely high pH (8.2 or greater) with a TA of 130. every time i add fill water, it drives my pH up, so I constantly have to add acid. In order to make this part easier, I converted my Stenner from LC injection to acid injection. To hopefully make life easier (and reduce impact on the adjacent equipment) I diluted the acid from 31.45% to 6.25% by putting 3 gallons of acid in a 15 gallon tank with 12 gallons of water. Here's where I am running into the math problem. I need to know if I run my fill water for X amount of time, how long do I have to run my injection pump to cancel out the change in pH from the fill water?


So here are my given values:
Pool Volume : 21000 gallons
Target pH: 7.4
Fill water pH : 8.2
Fill water TA: 130
Fill rate: 6 gpm
Acid Concentration: 6.25% (1/5 of 31.45%)
Acid injection .007 gpm

My next step, that I can't figure out, is how much will my fill water change my pH? If I run my fill for 30 minutes, that's an addition of 180 gallons of 8.2 pH water to a pool with 21000 gallons of 7.2 pH water. How do I calculate that change in pH?
And then say I run my injection pump for 1 hour, that's an addition of 1/5 of a gallon of 31.45% acid which should lower pH by .3

Thanks for any help you can provide

 

[crusemm]

Also, I am slowly driving TA down trying to get it back into the recommended range

 

[PoolStored]

How did you clean the tank for conversion? Just rinse it a bunch?

Thanks!

 

[crusemm]

At the end of last year, I pumped all of the remaining LC into the pool (there wasn't much left and it was pretty weak at that point) then i filled the tank with water and pumped that into the pool, then i stuck the hose in and walked away for a half hour or so. When that was all done, I dumped out the tank and then left it open for the winter. I also ran the Stenner pump dry to get all of the water out of the lines so they didn't burst in any winter freezes.

 

[cowboycasey]

Guess..

The best way I know.. start at running stenner for 1 hour a day.. Check your PH every day and log it for the week... Go from there raising or lowering the amount the stenner runs.. You PH will rise faster in the middle of summer as more water is being added and it will raise slower in the spring and fall..

 

[crusemm]

I think I may have diluted too much. 12 hours of pump run time is equivalent to one gallon of regular strength acid. so to change my pH by a measurable amount, I would have to run it for several hours at least.

 

[TexEdmond]

Guess..

Came here to say this. Going "off-label" like this won't be easy for any of us to figure out. Set yourself up a regular time to dose, document, and calculate. Buy your green lidded TA reagents in bulk. Make sure to keep the rest of us mad scientists in the loop with your results!

 

[crusemm]

I've found that if I run my stenner for 30 minutes (about 1/4 gallon of dilute acid) during a 1 hour fill (about 300 gallons) my pH and TA stay pretty stable. I had previously driven my TA down to about 90. So my TA is 90 and my pH is 7.8 with those run times. Pretty stable, and CSI stays around -.04

 

[TexEdmond]

I tried to convince myself that I "needed' an intellichlor about 3 times last season. I've got really high TA fill water too and was dosing something like 20oz of MA per day just to keep pH from continually heading to 8. Glad you found a solution that takes a bit of the labor off your hands.

 

[crusemm]

Still fine tuning. I should probably do some more empirical experiments, but right now don't have the time.

 

[TexEdmond]

Fair. My first season I thought I needed to be very precise with measuring and calculating. Now I just glug, wait, test, and if necessary, glug.