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Best Way To Reduce Ta?


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#1 Jeffbg

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Posted 23 August 2008 - 07:13 PM

My TA is pretty high by normal standards and I've only heard one way to reduce it and it seems unappealing. How do people typically reduce the TA in their pools?

-- Jeff



#2 Pool-newb

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Posted 03 September 2008 - 09:53 AM

Hey Jeff

I was able to lower my TA (total alkalinity) down after doing a lot of googling.

Small pool so it didn't take too long but it was kind of funny in a way.

The goal is to lower the PH and then areate the pool.
I lowered the pH with muriatic acid then used my shop vac (the same one I used to suction the sand out of the filter) connected to the blower side, and weighted the hose just low enough into the pool that the back pressure wouldn't stop it.

Wasn't really fast but it did work - several hours of running the vacuum. Had a great spa effect at the same time.


The next question was why the pool got to the high TA anyway.

Beginner that I was (three months ago now) and mud pond that it had become after a year off pump and 6 years of no care, the nice lady at the pool store sold me the chlorine tabs and the alk up and all kinds of other expensive stuff to throw in there.

But the tabs are acidic and that drops my pH.
Raising the pH also raises the TA.
So now I use liquid chlorine bleach which raises the pH - a lot less than the tabs lower it, and very small, seldom doses of muriatic acid to keep the pH in range.

I'll probably eventually have to add some alkalinity because my pump is sucking air and blowing lots of bubbles into the water.

I ordered a new pump yesterday.




~8,500 gal, ig, 12x24 vinyl, 1.5 HP Dual Speed Hayward Northstar, Wood-fired pool heater since Apr 09. Using Bleach and Muriatic Acid since I found CYA levels well above 100. Using electronic ORP/PH meter for testing as well as TF1000 DPD-FAS test kit for dosing. Got rid of major serious metal stains (TWICE now) from rusted out gas heater on the old vinyl liner . Poorly maintained till I got it. Apr 08. Here's what I did/do to revive and now maintain it:
- First went back to the pool school at Trouble Free pool and used the BBB method. I calculate the needed chemicals using The pool calculator
- Purchased and use a TF-100 from <link removed>
- Purchased Hanna pH/ORP for routine testing
- 25 May 09 installed SWG, and like it. ORP meters show negative numbers and are now not usable.

#3 chem geek

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Posted 03 September 2008 - 10:10 AM

Pool-newb's advice is spot-on. The procedure for lowering TA is described here. The procedure is also described in this post where you can see in a chart why the procedure works. Acid addition lowers both pH and TA but aeration raises pH with no change in TA. So the combination is what lowers TA. The aeration is most effective when the overall pH is lower.

Pools are intentionally over-carbonated so what you are essentially doing is accelerating the outgassing of carbon dioxide from the water. That happens faster at lower pH and with more aeration. The acid addition keeps the pH low. When you reach your TA target, you stop adding acid and just aerate to raise the pH. You never add any chemical (e.g. pH Up) to raise the pH during this procedure (doing so would end up raising both pH and TA).

It takes 3.2 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the Total Alkalinity (TA) by 10 ppm in 10,000 gallons. A larger pool requires proportionately more acid. You don't add the total amount of acid all at once, but add it to get to a low pH (around 7.0 or 7.2 depending on the next to lowest reading of your pH test). You can use The Pool Calculator to roughly estimate the amount of acid needed to lower the pH though this is only an estimate (my Pool Equations spreadsheet can calculate the precise amounts, but it is not for novice users). Whenever you add acid to the pool, or most forms of chlorine for that matter, you should do so pouring slowly over a return flow in the deep end with the pump running. For extra safety, especially with vinyl pools or above-ground pools with no floor drain, you should lightly brush the side and bottom of the pool to ensure thorough mixing after adding the chemical.

Richard

#4 Pool-newb

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Posted 08 September 2008 - 11:33 AM

QUOTE(chem geek @ Sep 3 2008, 02:10 PM) <{POST_SNAPBACK}>
Pool-newb's advice is spot-on. The procedure for lowering TA is described here. The procedure is also described in this post where you can see in a chart why the procedure works. Acid addition lowers both pH and TA but aeration raises pH with no change in TA. So the combination is what lowers TA. The aeration is most effective when the overall pH is lower.

Pools are intentionally over-carbonated so what you are essentially doing is accelerating the outgassing of carbon dioxide from the water. That happens faster at lower pH and with more aeration. The acid addition keeps the pH low. When you reach your TA target, you stop adding acid and just aerate to raise the pH. You never add any chemical (e.g. pH Up) to raise the pH during this procedure (doing so would end up raising both pH and TA).

It takes 3.2 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the Total Alkalinity (TA) by 10 ppm in 10,000 gallons. A larger pool requires proportionately more acid. You don't add the total amount of acid all at once, but add it to get to a low pH (around 7.0 or 7.2 depending on the next to lowest reading of your pH test). You can use The Pool Calculator to roughly estimate the amount of acid needed to lower the pH though this is only an estimate (my Pool Equations spreadsheet can calculate the precise amounts, but it is not for novice users). Whenever you add acid to the pool, or most forms of chlorine for that matter, you should do so pouring slowly over a return flow in the deep end with the pump running. For extra safety, especially with vinyl pools or above-ground pools with no floor drain, you should lightly brush the side and bottom of the pool to ensure thorough mixing after adding the chemical.

Richard


Yeah - thats what I just going to say biggrin.gif
I knew it worked pretty much like that, but thanks Richard for the detailed post.

I gotta mention here though that I practically burned up a leaf blower trying to figure out a good method to areate. The leaf blower had more volume but lower pressure and it was very sensitive to how deep the output hose was in the water.
The shop vac, on the other hand, worked well. It was also sensitive to the water depth but it could go much deeper and didn't seem to stress nearly as much when I kept it at the lowest usable depth. It is also important to make sure the hose and the filter in the vacuum are clean - it could get messy blowing all that gunk into the pool.

And it turns out that the sand and AlkUp I bought from the nice lady at the pool store were really usable after all.
After emptying the AlkUp bucket I filled it with some of the old sand out of the filter, added some water and it weighted the vacuum hose in the shallow end perfectly.



Btw, I did get that pump in, and replaced all the plumbing from the ground up.
It was an adventure so watch for a post about it in the next few days.




~8,500 gal, ig, 12x24 vinyl, 1.5 HP Dual Speed Hayward Northstar, Wood-fired pool heater since Apr 09. Using Bleach and Muriatic Acid since I found CYA levels well above 100. Using electronic ORP/PH meter for testing as well as TF1000 DPD-FAS test kit for dosing. Got rid of major serious metal stains (TWICE now) from rusted out gas heater on the old vinyl liner . Poorly maintained till I got it. Apr 08. Here's what I did/do to revive and now maintain it:
- First went back to the pool school at Trouble Free pool and used the BBB method. I calculate the needed chemicals using The pool calculator
- Purchased and use a TF-100 from <link removed>
- Purchased Hanna pH/ORP for routine testing
- 25 May 09 installed SWG, and like it. ORP meters show negative numbers and are now not usable.




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