Automatic PH Acid Math

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T

Tsteiny

Active member
Aug 29, 2022
34
Mesa, AZ
Pool Size
9600
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool SJ-20
So asking you guys that seem to be much smarter than me with chemistry and math. double check me please.

My pool uses 1 gallon of MA a week. I’m plagued with high TA for my water fill. With the 34.5% MA I am installing a automatic acid dispenser. I got a Stenner pump that operates at 0.89 ounzes per minute. I also have 15 gallon barrel for a 3 to 1 dilution. So… trying to get a rough estimate where to start, so here is my thinking…

I need 1 gallon a week which is 128 fl ounzes, divide by 7 days to get 18.3 ounzes of acid needed daily. 3 to 1 dilution would mean the pool needs (18.3oz acid, 54.9oz water) 73.2 ounzes of the dilution daily. The pump at 0.89 ounces per minute means it’s needs to run for 82.2 minutes (73.2 divided by 0.89).

Does the sound somewhat correct?
 
That’s what I thought too but ever since installing the SWG that’s what I average every week.

Right now it’s a struggle to get my PH below 8. I have no water features running and TA likes around 90. City water TA is 120 😳. I would like PH around 7.6-7.7. Every time I bring down the TA, it takes about 1-2 weeks to come right back up.
 
Normal TA water for our area. Your acid additions sound like you are using a low % acid. Check that.
The SWCG has little effect on pH rise. I suspect you used trichlor before, which is very acidic. If so, you have added acid all along. Just in a different form.

For comparison, I add about 12 oz of 31.45% muriatic acid to my pool during the high evaporation times. That would equate to about 18 oz a week for you. And your evaporation rate is less than mine.
 
I did use trichlor previous. I installed the SWG last year and then had to do a slam, been fine ever since then.

I use 31.45% acid from Home Depot. Been using that for a good 6 months.
 
OK -- so 1 gallon of MA a week is reducing your TA by 52 ppm. You would need to be adding several thousand gallons of water each week from evaporation to need that much acid. Something does not add up ------
 
Interesting…. Just went out to check. The 4 bottles I bought where the 14.5% 🤦🏻‍♂️. Oh well, still like to automate it because I travel a lot and the wife does a good job monitoring it but don’t want her adding chemicals.
 
I would still suspect a gallon of the 14.5% per week is too much. But closer to reality.

You can automate it. Just takes equipment. Still have to test and adjust as the seasons change.

When we leave for more than a week or so in the summer I have a gallon jug marked off in 4 ths. I mix one quart of 31.45% and the balance water in it. From my historic testing, I know I need about 8 oz of acid every 4 days. So I have a neighbor come over and dump one fourth of the jug in the pool every 4 or 5 days. It keeps the TA from getting too high by managing the pH.
 

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Let your TA come down to 60. It may take a while with our 120-130ppm TA fill water.
Do NOT add baking soda or any alkalinity up product. A TA of 60-70 is perfectly fine and will slow your pH rise. The higher the evap rate, the more the TA will increase because of the high TA fill water.

Fill out your signature with pool, pool equipment (including manufacturers and model numbers) and test kit info.
This assists us in providing help based on your specific pool without needing to ask each time.

Post a full set of current test results from one of the recommended test kits.

FC
CC
pH
TA
CH
CYA
Salt
Water temperature
 
All the pool info is in the top of my profile already.

Test as of this morning:
FC 7.4
CC 0
pH 7.3 (added acid last night)
TA 70
CH 420
CYA 70
Salt 3600
Temp 79

Normally when I add the acid pH comes down to mid 7’s and TA comes into the 70’s too. Within a few days, I’m back up to 8 and TA back to 80-90. I try to get TA to come down to 60 but I have to add acid everyday and the pH was getting to 7.0 (with my waterfall running too) and again, about 2 weeks later, TA is back up to 80. Got a pool cover on for the last few weeks and no leaks in the pool.

I got all the equipment for the acid dispenser already for $300. Too me it’s worth to not have to deal with it all summer besides checking chemicals once or twice a week once I got it dialed in.
 
TA is added by fill water or chemicals. If your pool is covered, there is minimal fill water. So there should be no TA increase.
 
Sounds like the acid dosing will be very helpful for you and give you peace of mind while away.

I'm thinking that after a few months watching the numbers you'll find you can settle with a target pH of around 7.7 or even 7.8 and TA around 80 to 90 ppm. That could change as your calcium hardness rises, so watch for that down the track.

Kudos again on the injector calculations... Just for fun, I'm predicting 20 minutes per day of 31.45% as diluted 3:1 per your original plan.
 
I realise this post is a few months old now. However something isnt adding up.
All the pool info is in the top of my profile already.

Test as of this morning:
FC 7.4
CC 0
pH 7.3 (added acid last night)
TA 70
CH 420
CYA 70
Salt 3600
Temp 79

Normally when I add the acid pH comes down to mid 7’s and TA comes into the 70’s too. Within a few days, I’m back up to 8 and TA back to 80-90. I try to get TA to come down to 60 but I have to add acid everyday and the pH was getting to 7.0 (with my waterfall running too) and again, about 2 weeks later, TA is back up to 80. Got a pool cover on for the last few weeks and no leaks in the pool.

I got all the equipment for the acid dispenser already for $300. Too me it’s worth to not have to deal with it all summer besides checking chemicals once or twice a week once I got it dialed in.
Click to expand...

The Total Alkalinity cannot increase on its own. Are you adding a weekly shock dose of chlorine? Salt chlorinators do not increase TA (despite what pool shops may say). Something is increasing it.
 
It’s increasing because the TA in the city water in this area is 120. I tested it twice.

If anyone is curious, I installed my acid dispenser and it’s awesome! I love it. Got it dialed in and it holds around 7.5ish pretty reliably. I got about 3 months of acid it seems with me doing nothing but slight changes when it gets hotter and evaporation is higher.
 
Thanks for this thread! I bought all the parts to install an acid feed pump a while back, then got lazy and haven't followed through. Now I'm feeling more motivated.

I also have a SWCG and makeup water that's > 100 TA. My pool consistently needs about 1/2 gallon of muriatic acid each week (a little less in the winter).

I use the Taylor acid demand test to determine how much acid to add. In my experience, adding HCl does result in the predicted pH decrease but does not lower TA nearly as much earlier posts in this thread say it should.

My understanding was the SWCG effectively splits HCl into hydrogen gas and chlorine (via NaCl) and many of the hydrogen ions are being lost to the atmosphere in the form of bubbles rather than being neutralized by bicarb. But in any event, it seems the weekly pH decrease is temporary and HCl and NaHCO3 aren't fully reacting. It's also worth noting that the pool gets to 7.2-7.4 immediately after I add the acid, but it always drifts back up to 8 by the next week so the pool water spends much of its time at a higher pH.

I'm not a chemist so I don't know what's happening, but those are my observations.
 
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