Reduce Total Alkalinity Levels

[all4him]

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

[LJR]

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]

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]

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]

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!!!

[Buggsw]

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]

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]

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]

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]

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

[ml001]

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.

If my goal is to lower TA without lowering PH, do I want to have pump running? I was told by pool dealer that circulating the water in this (acid column) process would only cause the acid to spread out and lower PH more than desired...

Sorry in advance if this has already been addressed. I'm trying to read enough to catch up!

[chem geek]

The "acid column" or "slug" method is debunked in this technical report. It's just not very effective because the ONLY way that TA gets reduced is through the outgassing of carbon dioxide out of the water. Pool are intentionally over-carbonated in order to provide a pH buffer and to protect plaster surfaces. Think about a carbonated soft drink you want to make flat. How can you make that happen faster? You can blow bubbles into it or stir it up to agitate it -- that is, you can increase aeration. You can also add acid to it and will get more bubbles that way just as you do when you add vinegar to baking soda (which is sodium bicarbonate that is mostly the TA in your pool). A pool is not as carbonated as a soft drink so you won't actually see bubbles, but the principle is exactly the same.

With the correct TA lowering procedure shown here you intentionally want your entire pool to be at low pH so that the outgassing of carbon dioxide over the entire pool surface is maximized. When the pH of the pool is low (say, 7.0), then aeration and this low pH maximize the rate of carbon dioxide outgassing. When this happens, the pH rises with no change in TA (for technical reasons I won't get into here). You then add acid to keep the pH low and adding acid lowers both pH and TA so the net result over time is a lowering of the TA. This chart shows the relative rate of carbon dioxide outgassing where you can see that lower pH has a huge effect (obviously though high TA also outgasses faster, you don't want to increase the TA in order to reduce it!).

You can aerate the pool more by turning up the returns and having the pump on high speed. You can also use devices like this one and can use a pool cover pump with a shower or can turn on any water aeration features you have such as waterfalls or spillovers or just get a bunch of kids to splash like crazy (they will find the water may sting their eyes at the lower pH, but it's still safe to swim in). If you have an air compressor, then hooking it up to a pipe with small holes or a nozzle that produces many tiny bubbles works really well by putting that into the deep end. The key is having lots of small bubbles exposed to the water for a long time before they reach the surface (this maximizes carbon dioxide exchange). Agitating the surface to break the surface tension also helps.

When you add acid to the pool, or most any concentrated chemical (that quickly dissolves) for that matter, you should do so very slowly over a return flow with the pump running, preferably in the deep end.

It will take the same cumulative total amount of acid to lowe the pH regardless of how it is done or how long it takes or what the TA level is. It takes 25.6 fluid ounces (3 cups, 1.6 ounces) of Muriatic Acid (31.45% Hydrochloric Acid) to lower the TA by 10 ppm in 10,000 gallons (it takes more in a larger pool; less in a smaller pool). The amount of acid it takes to initially lower the pH to 7.0 (or 7.2) depends on the starting pH and the TA level.

Richard

[Larry]

The first post in this thread has been updated to reflect the superiority of the acid + aeration method over the historical acid slug method.

[Guest]

I'm new to the forum but not pools. My question, other that causing the PH to creep up, what other adverse condition does a high TA cause? I have an indoor 15,000 gal fiberglass pool with the TA at 510 and the PH is 7.4. I have aeration built into the pool so I'll try the aeration/acid method. My pool shop suggested the "slug" method.
I have well water with a lot of metal, and staining is also an issue. I use "metal out" as a maintenance item and "citric acid" to remove the stains and it's MAGIC. I use 68% Calcium Hypoclorite because of over stabilation issues. Any advice will be appreciated!
I'll definitely be spending time on this forum.

[hiperf2007]

New pool. Sick and tired of listening to everybody at HTH give me advice on my pool chemicals. Bought a new quick pool for my daughter this summer. After clearing up the brown crap from well water my readings are way off the chart. Chlorine was 0, PH was 7.8, TA was 240+?, CYA was 30-50. 5 people now told me to use muriatic acid to lower the pools TA. They told me to start with the TA because that was the most important thing to start with. I went on here and found a calucator tell me to lower the pools TA 100PPM, it would take 2240ML of muriatic acid. I take it my TA is over 240 because I tried PH Minus twice now with no drop. I went ahead and added 2240ML - 10CUPS to my pool now to do more reading saying that was to much to add to a pool. Some people dont recommend using muraitic acid in vinyl pools. Too late I guess. 2-3 hours later, the TA is still 240+ and now my PH droped to 6.4 or lower. I think the CYA is now 0. Should I just pack the pool up and take it back? I'm tired of this. The water is nice and clear now after spending $90 on a filtering system to filter out the metals in my water.