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.
ml001
Pool Newbie
Pool Newbie
Posts: 1
Joined: Sat 17 May, 2008 12:05

Postby ml001 » Sat 17 May, 2008 12:55

chem geek wrote: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
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Reduce Total Alkalinity Levels

Postby chem geek » Sat 17 May, 2008 13:45

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
User avatar
Larry
Pool Forums Admin
Posts: 371
Joined: Thu 09 Dec, 2004 20:19
My Pool: Inground concrete 72m2
Tiled overflow pool
2 Hp pump mono
Fiberglass sand filter 920mm
Tiled deck

Reduce Total Alkalinity Levels

Postby Larry » Thu 05 Mar, 2009 09:20

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

Reduce Total Alkalinity Levels

Postby Guest » Thu 04 Jun, 2009 13:09

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. :thumbup:
hiperf2007

Reduce Total Alkalinity Levels

Postby hiperf2007 » Sun 14 Jun, 2009 17:06

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.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Reduce Total Alkalinity Levels

Postby chem geek » Mon 15 Jun, 2009 00:41

Acid lowers both pH and TA. The acid will lower the TA regardless of how it is added, but to raise the pH back up without raising the TA one aerates the water at lower pH. That is, aeration + acid at low pH is more efficient and less dangerous since it doesn't pool concentrated acid in one place. You do NOT, however, add all the acid at once. As noted in the procedure at the start of this thread, you add enough acid to lower the pH to 7.0, not all the acid amount needed to lower the TA all at once. Also, when adding acid to a pool, one should do so SLOWLY over a return flow with the pump running and then, especially in vinyl pools, lightly brush the side and bottom of the pool to ensure thorough mixing.

hiperf2007, who is measuring your TA? Is it the pool store or is it by using test strips? The CYA should not change from adding the acid. You should get your own good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 at tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

It takes around 3.2 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the TA by 10 ppm in 10,000 gallons. What calculator did you use that said 10 cups would lower the TA from by 140 (from 240 to 100)? In 10,000 gallons, that would take about 44 cups, but NOT added all at once. Since your pH presumably dropped a lot, then either your pool is a lot smaller than 10,000 gallons or your TA is no where near 240. Again, get your own test kit to find out the truth.

If your pH is truly as low as claimed, then you can raise it without raising the TA as much (assuming the TA is in fact too high, which is questionable) by using 20 Mule Team Borax or you can aerate the water if that seems to work. You could use pH Up, but it will increase your TA. Again, use your own test kit if you can.
hiperf2007

Reduce Total Alkalinity Levels

Postby hiperf2007 » Mon 15 Jun, 2009 09:42

My pool is only 4000 gallons. http://www.havuz.org/pool-calculators.htm#hydrochloric is the website I used for figuring out what I should add. Pool size 14,000 litres, Desired reduction (over 100) 100 is the highest. I do test with strips. I have never seen anything under 240. So I put in 100PPM. Nothing said not to add all at once. I was told to leave the pump on and dump it in the water, so that is what I did. I did mix it around good and let the pump run all night.
hiperf2007

Reduce Total Alkalinity Levels

Postby hiperf2007 » Mon 15 Jun, 2009 09:55

hiperf2007 wrote:My pool is only 4000 gallons. http://www.havuz.org/pool-calculators.htm#hydrochloric is the website I used for figuring out what I should add. Pool size 14,000 litres, Desired reduction (over 100) 100 is the highest. I do test with strips. I have never seen anything under 240. So I put in 100PPM. Nothing said not to add all at once. I was told to leave the pump on and dump it in the water, so that is what I did. I did mix it around good and let the pump run all night.



I went out and dropped a strip. I added enough acid to pretty much "techincially" drop the PH from 7.4 to around 3, but here are my results after 12 hours.

Harness 1000 (+)
Chlorine 0
PH 6.8
TA 240 (+)
CYA 0

10 cups of muriatic acid in 4000 gallons didn't lower the TA, how damn high is it? I delutited it 2 cups at a time in 1 gallon milk jugs and walked around the pool and dumped it in with the pump running. Some people say the pump off and in one stop, but then the next site says pump on, even out the acid.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Reduce Total Alkalinity Levels

Postby chem geek » Mon 15 Jun, 2009 16:00

I wouldn't trust the test strips. If the TA was truly that high, then the water would tend to rise in pH if you took out any Trichlor tabs (which are acidic), especially if you aerated the water some.

As you've learned, you don't want to add so much acid as to lower the pH much below 7.0, especially in a vinyl liner pool as low pH is the worst thing for a vinyl liner (as well as metal). If your pH is still low, I'd at least raise it to 7.0 for now. To raise the pH with only half as much rise in TA, use 20 Mule Team Borax (instead of pH Up).

How did your Hardness get so high? With test strips, you can only test Total Hardness (TH), not Calcium Hardness (CH) which is what you really want to measure. Have you measured the TA and TH of your tap water? Is it well water? Oh yes, I see that you said that it was indeed well water. Well, that can explain the high hardness and even high TA. However, with high TA you should have seen the pH tend to rise.

I strongly suggest you get yourself a good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

If your TA and CH were truly that high, then getting the pH into normal range would likely lead to calcium carbonate scaling. Have you been using Cal-Hypo from HTH as your source of chlorine? Perhaps that is the problem since it increases CH. The following are chemical facts for chlorine sources independent of concentration and pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.
hiperf2007

Reduce Total Alkalinity Levels

Postby hiperf2007 » Mon 15 Jun, 2009 19:18

Where do you find this 20 Mule Team Borax? I have been on the phone about once a day with HTH on where to go with this pool. I walked out and dripped a stip again and it showed the following:

TH 1000
FC 1/2
PH 6.4
TA 240
CYA 0

The PH was up this morning too 6.8 but then it rained for about 45 minutes today. I don't know if that has anything to do with it but now it's back down to 6.4. I was thinking about just heading over to walmart for some PH Plus. HTH told me the most important things are the Chlorine and the PH. They said some people call in forever dealing with high hardness and high alkalinity and it seems some people just have a hard time bringing it into range and controlling it. I bought a $175 pool for a my daughter this summer and I have spend over $200 in chemicals and getting nothing. I told the guy on the phone I was about ready to pack the pool up and take it back and purchase a summer pool pass to our town indoor pool. :roll: Thats when he told me well the most important things are Chlorine and PH for water safety. I have though about getting some PH plus and getting it up to 7.2-7.5 and being done with it.

Return to “pH & Total Alkalinity”

Who is online at the Pool Help Forum

Users browsing this forum: No registered users and 0 guests