TA at 1100-1200 ppm!

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
cocktailking
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My Pool: TigerSpa jacuzzi approx 2m cubed, 36 degrees, paper filter, passive heater.
Location: Canary Islands

TA at 1100-1200 ppm!

Postby cocktailking » Mon 27 Apr, 2009 09:04

High, i live on a volcanic island, and have struggled to reduce the TA of my jacuzzi. Have being going at it incrementally for about 4 weeks.
The Local water board tells me the TA is between 1100 and 1200. How much Acid (26%) am i likely to need in total to get it down to maybe 150pm, and how much can i put in at a time?


chem geek
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TA at 1100-1200 ppm!

Postby chem geek » Mon 27 Apr, 2009 09:42

It takes 10.8 fluid ounces of 26% Hydrochloric Acid in 350 gallons to lower the TA by 100 ppm and the amount of acid should be scaled by tub water volume. Since you would not add all the acid at once since that would get the pH too low, it will take a lot of cycles down to 7.0 and aerating to get the pH up and then adding more acid. Are you absolutely sure their numbers for TA are correct? The water would have a tendency to get to a very high pH when exposed to air, probably close to 8.5 or so (though could keep rising to 9.4 before stopping completely). If there is any sort of Calcium Hardness (CH) in the water, then scale will likely precipitate.
cocktailking
Pool Newbie
Pool Newbie
Posts: 3
Joined: Mon 27 Apr, 2009 08:59
My Pool: TigerSpa jacuzzi approx 2m cubed, 36 degrees, paper filter, passive heater.
Location: Canary Islands

TA at 1100-1200 ppm!

Postby cocktailking » Mon 27 Apr, 2009 14:23

Thanks for replying.
Well, the figure of 1100-1200ppm has come from the local water authority, whom i sincerely hope know what they are talking about! (i do say hope)
Having read the advice and made the calculation from this website, i have been adding about 100ml of acid every 2-3 days, and testing. I´ve probably added about 1.5 litres in total, and still have a TA higher than the strips will give an accurate result, and a pH somewhere over 8.5 (again the strips and tablet tests dont give accurate results over these quantities). I have been using more chlorine than normal (as you would expect with a high ph and TA) but i´m also using magnets on the pipes, so the water is always lovely and clear (whether this is the magnets is of course up for debate).
I understand the relationship of pH is logarithmic, so it only makes sense to me to need a significant quantity of acid to bring it down from a very high level.
I was really wondering if anyone else had any experience similar (maybe the hawaiian islands), and if anyone could tell me how much acid was safe to add, and how often.
Any hints/tips etc would be greatfully received.
P.S i do get quite alot of chalky bits in the bottom of the spa.
chem geek
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TA at 1100-1200 ppm!

Postby chem geek » Mon 27 Apr, 2009 21:10

When the TA is very high, it takes a LOT of acid to lower the pH. Probably the best thing for you to do is to get the Taylor K-2006 test kit you can get at a good online price here . It contains acid and base demand tests that will tell you exactly how much acid it will take to get from your current pH to any pH that you can see in your test, such as 7.0.

The chalky bits are most likely calcium carbonate scale. That's not good since this could be forming in your heat exchanger (I wouldn't use it or heat the water until you've gotten the water in balance) or on other parts of your jacuzzi. I also would only use the circulation pump and not the jets until you get the pH down -- otherwise the aeration will continue to raise the pH and at this point you want the pH lowered before you do any aeration.
cocktailking
Pool Newbie
Pool Newbie
Posts: 3
Joined: Mon 27 Apr, 2009 08:59
My Pool: TigerSpa jacuzzi approx 2m cubed, 36 degrees, paper filter, passive heater.
Location: Canary Islands

TA at 1100-1200 ppm!

Postby cocktailking » Tue 28 Apr, 2009 03:57

Thanks alot for your help. Days worth of search wisdom relayed in a couple of paragraphs.
I shall go ahead and order the accurate testing kit.
One thing i´d still like to clarify, since i´ll be dealing with alot of acid addition, is how much acid (26%) can i add at any one time, and how frequently can i add/test it?
chem geek
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Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

TA at 1100-1200 ppm!

Postby chem geek » Tue 28 Apr, 2009 09:57

You can add as much acid as the acid demand test says you can. This will vary depending on your starting and target pH and your starting TA. As your TA drops, you'll add less acid during each cycle. You add more acid when the pH rises so if you are doing the aeration and acid addition at a pH of 7.0, then when the pH rises to at least 7.2 you can add more acid to get it back down to 7.0. During the early stages, it's likely your pH will rise higher than that more quickly.

For your first acid addition, I'd add half of whatever the acid demand test tells you, just to be safe. After you gain some more experience, you can trust the acid demand test more.

You did not tell me the size of your jacuzzi, but if it's 350 gallons with a TA of 1150 ppm, then to go from a pH of 7.5 to 7.0 would take about 13 fluid ounces of 26% acid and this will lower the TA by 122 ppm. When the TA gets down to 200 ppm, it takes only 2.4 ounces of acid to drop the pH by the same amount and this lowers the TA by only 22 ppm. So you can see that it will take quite a few cycles to lower the TA.

Richard

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