Reduce Total Alkalinity Levels

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
all4him
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Reduce Total Alkalinity Levels

Postby all4him » Fri 04 May, 2007 07:01

Are you saying poor the acid directly into the pool or should it be mixed with water per the instructions on the bottle?


LJR

Total Alkalinity in Vinyl Pool

Postby LJR » Mon 18 Jun, 2007 18:53

You have recommended slugging acid to reduce total alkalinity in a hard surface pool. What do you recommend for a vinyl lined pool? My TA is running about 250 with a PH of 7.2. Should I try raising Ph with Borax and lowering it with dilute acid?
Backglass
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Reduce Total Alkalinity Levels

Postby Backglass » Mon 18 Jun, 2007 21:18

It's all a myth folks. Actual testing by real, live scientists shows that how you add the acid (trickle, slugging, acid column, etc) makes no difference.

From the Journal of the Swimming Pool and Spa Industry:

www poolhelp com/JSPSI_V1N2_16-30_AcidColumn.pdf
Buggsw
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Reduce Total Alkalinity Levels

Postby Buggsw » Mon 18 Jun, 2007 23:04

One study says that, others don't and I beg to differ.

In my experience - and I just went through this with my own pool - Using the acid slug/column/ball method lowers TA quicker with less disruption to pH versus drizzling/trickling/dribbling acid - which lowers pH more than TA.

I spent 2 weeks fiddling with using both methods. I couldn't get my TA to hardly budge using the drizzle method and I spent hours and hours aerating to get my pH up to do it again, by which time my TA also rose a bit. However, whenever I used the acid ball method in 2 or 3 spots while my water was calm, my TA would drop 5 to 10 ppm and my pH would barely drop.
Backglass
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Reduce Total Alkalinity Levels

Postby Backglass » Tue 19 Jun, 2007 08:12

Buggsw wrote:One study says that, others don't and I beg to differ.

In my experience - and I just went through this with my own pool - Using the acid slug/column/ball method lowers TA quicker with less disruption to pH versus drizzling/trickling/dribbling acid - which lowers pH more than TA.

I spent 2 weeks fiddling with using both methods. I couldn't get my TA to hardly budge using the drizzle method and I spent hours and hours aerating to get my pH up to do it again, by which time my TA also rose a bit. However, whenever I used the acid ball method in 2 or 3 spots while my water was calm, my TA would drop 5 to 10 ppm and my pH would barely drop.


Yes, but without two identical pools to test on, how do you know that your two weeks of drizzling didn't affect the later acid ball? It's like when you can't get a lid open on a jar and you hand it to someone else and they pop it right off. Did you loosen it? Or were they stronger?

I DO know that when I wear my lucky underwear, the Yankees always win however. I've seen it happen!!! :lol:
Buggsw
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Reduce Total Alkalinity Levels

Postby Buggsw » Wed 20 Jun, 2007 01:09

Well, because since then, when I drizzle to adjust pH the TA still doesn't move much at all.

Over time the TA drifts upwards (because my fill water has high TA)
The acid ball will always bring the TA down a lot more and barely affect the pH.
chem geek
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Aeration & lowering Total Alkalinity

Postby chem geek » Thu 21 Jun, 2007 21:39

Neither the acid ball slug method nor the drizzling method are the same thing as lowering the pH significantly and then adding aeration while adding acid to keep the pH low. Even if the acid ball slug method is somewhat more effective at lowering TA (and this is controversial), it is not nearly as effective as low pH with aeration. This is the fastest way to lower TA -- guaranteed. It is the following procedure. Note that you should use the next to lowest measurement on your pH test kit as the low-end -- so if your pH kit only goes to 7.0, then use 7.2 as the low-end target and 7.4 as the high-end trigger to add acid to get back to 7.2.

ACTIVITY .......... pH .... TA ... The following assumes 6.8 is the lowest measurement on the pH test kit
==================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2
Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)
-----------------------------------
Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

==================
Net of Above ....... 0 ........ -

Note that there is NO addition of base (Borax or otherwise) in the above procedure. Aeration would include running your SWG, running your waterfall, adding any fountains or other aeration features, getting an air compressor with a nozzle or pipe with small holes that produces tiny bubbles and putting that in the deep end of the pool, etc. By the way, rain is an excellent aerator with splashing drops, but unless you can control the weather...

The above procedure works because the rate of outgassing of carbon dioxide from a pool varies with pH and TA level and with aeration. Pools are intentionally over-carbonated -- that's why you initially add sodium bicarbonate / baking soda / Alkalinity Up on pool startup (unless your fill water is already high in Total Alkalinity). Think of the pool as a carbonated beverage -- it will outgas carbon dioxide. Stirring up (aerating) your drink causes more carbon dioxide to release faster. If you blow bubbles through a straw, the drink goes flat (loses its dissolved carbon dioxide) quite quickly. If you measured the pH and TA of your drink, you would find that as carbon dioxide is released, the pH rises with no change in TA. The same happens in a pool (for technical reasons I won't get into here).

This chart shows the relative carbon dioxide outgassing rate at various pH and TA levels. This is a relative rate since it is also a function of aeration, wind, etc. and that is not easily quantifiable. You can see how lower pH significantly increases outgassing. That's what makes the above procedure go faster, along with aeration. The outgassing rate also determines the amount of acid you would need to add over time to restore (lower) the pH. So running your pool at lower TA and higher pH will lessen the need for acid addition over time.

This chart shows the relative rate of pH rise at various pH and TA levels. Though the lower TA has a lower outgassing rate, it also has a lower pH buffering effect and these tend to cancel each other out though the outgassing effect is slightly stronger. This is why you can see some lowering the the pH rise at lower TA though running at a higher pH target is more effective (so most people do both -- lower their TA level AND target a higher pH).

Richard
Carllieb

Areation

Postby Carllieb » Mon 25 Jun, 2007 16:17

For areation I have found that I can take a 3/4 nipple add a couple of 90 deg elbows and a length of pvc to bring it above the level of the pool.

Just jam the nipple into the return and either aim the pvc up for a fountain effect or bring it above the level and 90 it into a jet.

The pvc does increase back pressure but not enough to cause problems and the areation is awesome.

In addition my kids love playing in the jet of water.
Guest

Reduce Total Alkalinity Levels

Postby Guest » Sat 15 Sep, 2007 07:30

I am dealing w/ a very similar situation here on my end. One question I have is, I have seen it mentioned somewhere on this site to allow 3 days for the additional acid added to fully seat in the pool water. Using the above directions, am I to wait the 3 days before adding more acid or can I just follow the steps as described?
chem geek
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Reduce Total Alkalinity Levels

Postby chem geek » Sat 15 Sep, 2007 18:32

It does not take 3 days for the acid to affect the pH and TA levels in a pool. The chemical equilibria are relatively fast. I've added acid and tested my water at the other end of the pool and within a half hour I get the expected amount. This assume the pump is running and you have good circulation.

As for the steps in the TA lowering procedure, you do not need to wait between them. Aeration can be going on the entire time. You can add acid at the same time you are aerating. For testing pH again, you want to wait for it to come up from the aeration and that is much harder to know how long it will take. That's something you just need to adjust as you go along. Test after an hour or two of aeration and see if you notice a pH rise. If not, try 4 hours, then 8. If the aeration isn't vigorous or the pH isn't low, then the rate of pH rise from aeration will be slow. With an air compressor, it's usually relatively fast, rising measurably within an hour.

Richard

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