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Lowering Total Alkalinity -- Howto

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I wrote this guide on lowering TA because there was not one for pools and the one in the hot tub water chemistry by Nitro, while excellent, is really geared toward hot tubs and spas! The info here is applicable to both, however!

If you just want the "howto" on lowering TA (Total Alkalinity) scroll down to the blue text at the end of this post. However, I strongly suggest you read all of the post since it explains WHY this works! It might look long but I've kept it very simple!

There is a persistant myth in the pool/spa industry that you can lower TA by adding "slugs" of acid to the pool with the pump off and if you "walk" the acid around the pool with the pump on you will lower pH. This is pure rubbish. Any addition of acid, slugs or otherwise, will lower the TA AND the pH. Period! In addition, adding slugs of acid can damage the pool surface and adding enough acid all at once to drop the TA can lower the PH far enough to cause other damage and problems with pool equipment. IF you want more info here is scientific paper for a detailed study showing why "slugging" vs. "walking" acid is bogus! Here is a less technical summary paper.


If you want the answer then read on!cool.gif

In a nutshell this is all you have to do:

1. Add acid to lower your PH to between 7.0 and 7.2 (this also lowers TA) then test your TA

2. Aerate until PH rises to around 7.6 (the only way to raise PH without also raising TA)

Repeat steps 1 and 2 until you reach the desired TA.

IF your TA is very high it might not seem like anything is happening at first but keep doing this and you will find that you will lower your TA!

To give you some numbers let's say that you have a 15000 gallon pool and your TA is at 180 ppm and you want it at 80 ppm (a 100 ppm decrease). You will need about 3 gallons of 20 baum (31%) muriatic acid or about 33 lbs of dry acid to do this but if you put it in all at once you will drop your pH by APPROXIMATELY 6! THIS MEANS THAT IF YOU START OUT AT A pH of 8.0 IT WILL BE ABOUT 2.0 AFTER ADDING ALL THE ACID! This is low enough to cause damage. In addition, if you "slug" the acid in the deep end with the pump off you will have a concentrated pool of acid sitting on the pool bottom for an extended period of time, which will be bad for ANY pool surface, be it plaster, vinyl, or fiberglass!

No problem you say, just add some pH increaser (soda ash). That won't work because pH increaser ALSO CAUSES TA TO RISE VERY QUICKLY BECAUSE IT ADDS CARBONATE IONS TO THE WATER WHICH THEN CONVERT INTO BICARBONATE IONS (WHICH IS WHAT TA REALLY IS, A MEASURE OF HOW MUCH BICARBONATE IS IN THE WATER!) If you try this you get caught on the lower the TA, now my pH is too low, raise the pH, now my TA is even higher than before merry go round!

(Even those of you who think you are chemically aware and say "I will use borax instead of pH increaser since it doesn't have that much impact on TA" will be wrong because any chemical method of raising pH WILL CAUSE TA TO RISE AGAIN! I am not going to get into the chemistry here since I want to keep it simple but if you really want an explanation let me know and I will post one in a separate topic. I warn you, it will NOT be basic basic and a knowledge of chemistry is going to be needed.blink.gif I will try and keep it as simple as possible, however! :rolleyes:)

Using the same example of a 15000 gallon pool with a TA of 180 ppm and a pH of 8.0 we would need between 3/4 and 1 gallon of 20 baum muriatic acid or a bit less than 9 lbs of dry acid to lower the pH from 8.0 to 7.0! This the the maximum amount we can really add safely at one time and now we are stuck with a pH of 7.0 which is livable but still a bit low. We have also only lowered the TA by less than 30 ppm at this point, not nearly enough! What to do?

So, how can we safely get this much acid in the pool at once to lower our TA down to where we want it? We can't!

So, what to do? It seems there is no answer to our dilemma!

But there is and it's really pretty easy.wink.gif We only add enough acid at one time to lower the pH to 7.0 and not any lower and then we need a way to raise the pH WITHOUT AFFECTING THE TA.

How can we do that? One word...aeration!

Let me explain. (And for any of you that want to debate the chemistry let me say that I am keeping it as simple as possible but what I am saying is basically correct, even though I am making some assumptions that are not completely true such as carbonic acid and dissolved carbon dioxide being the same. For our purposes here and the sake of a simple explanation, however, they basically are! I am also ignoring any contributions to the TA by cyanurates or borates since at their normal recommended levels these contributions are minimal.)

TA is a measure of the amount of bicarbonates in the water. That is really all we are measuring since, at normal pool pH there is practically no carbonates in the water. Besides bicarbonate there is also carbonic acid (carbon dioxide dissolved in the water) present. This is the buffer system that helps keep our pH in line The ratio between the amount of carbonic acid/bicarbonate is pH dependent. The higher the pH the higher the bicarbonate ions and the lower the carbonic acid. The lower the pH the lower the bicarbonate ions and the higher the carbonic acid (operative word here is acid! Lower pH means there is more acid in the water.)

Our pools and spas are purposely over carbonated! (Think seltzer).

When we add acid and drop the pH we convert bicarbonate to carbonic acid (carbon dioxide in water). If any of you doubt this just pour some vinegar (acid) on baking soda (sodium BICARBONATE) and watch it fizz (release carbon dioxide).

So, the simple act of adding acid to our water lowers TA (the bicarbonates) since we don't measure the amount of carbonic acid with our TA test. We also know that we do not want to drop the pH below about 7.0 since lower pH can cause all kinds of problems for us. THIS is why your test kit has an acid demand test! (You did take our advice and get yourself a GOOD test kit, right?)

So the problem becomes "how do we get the pH to rise without causing the TA to go back up?" We know that if we add a chemical pH increaser it will cause the TA to go back up because we are chemically converting carbonic acid back into bicarbonates (and adding additional carbonates if we are using the usual pH increaser, sodium carbonate!) This is a no win!

How can we lower the amount of carbonic acid? (operative word here is acid) Remember that I said to think seltzer? If we let a bottle of seltzer sit open it will eventually go flat. If we shake up the bottle (aerate the seltzer) it will go flat faster!

Now, IF YOU TEST THE pH OF THE SELTZER BEFORE IT GOES FLAT AND AGAIN AFTER YOU WILL FIND THAT THE pH HAS GONE UP! This is because the amount of (carbonic) acid in the water is now less! It has gassed off into the atmosphere as carbon dioxide (and has not been converted into bicarbonates so the total alkalinity of our seltzer has not increased!)

The same is true for your pool or spa. If you just drop the pH to 7.0 it will eventually climb back up as carbon dioxide gases off into the atmosphere. As the carbon dioxide gases off the amount of carbon dioxide dissolved in the water (carbonic acid) decreases BUT THE TA REMAINS THE SAME! As the amount of carbonic acid (operative word is acid) decreases the pH rises!

However, this is a slow process and we need to speed it up by shaking up our bottle of seltzer! Er, I mean by aerating our water! (You really can't put your finger on the top of your pool and shake it up, can you?tongue.gif)

Now the question is, how to aerate? The answer, any way that you can and the better you aerate the faster this process goes.

One of the easiest ways is to get a floating fountain that attaches to a return for a pool or turn on all your jets, aerators and bubblers for a spa. If you have a spillover pool/spa combo just turn on all the spa aerators and jets and let it spill into the pool. Turn on any water features that you might have (waterfalls, deck jets, fountains, etc.)

Adjust all your returns and jets to break the surface of the water!

Throw 10 neighborhood kids in the pool and have them all start splashing! (Don't worry, a pH of 7.0 is not going to hurt them at all!

I have heard of people taking an air compressor and using it to bubble the water like a giant airstone in an aquarium!

I have heard of people making a right angle fitting for a return out of pvc fittings and pipe to shoot the water in the air like a giant fountain.

Anything that will break the surface of the water and agitate it will work. The more vigorous the faster the process.

Combining more than one of the above is certainly going to be more effective than just one.

I think you all get the idea.

So, to summarize and put it all into a step by step guide:

1. Get together the things you need:

a. a good test kit that will test acid demand and TA (I recommend a Taylor K-2006 for chlorine and a K-2106 for bromine but, for adjusting TA, the K-2005 has exactly the same acid demand and TA tests and will perform equally for this purpose)

b. a way to aerate the water (water feature, floating fountain, built in jets and bubblers, returns adjusted to break the water surface, a bunch of kids or adults to have a 'splash party', etc.)

c. a bit of patience! (very important since this process can take several days to a few weeks if the TA is very high initially and your aeration method is not the most efficient!)

d. enough acid to complete the process, usually a lot more than you think you will need!blink.gif

2. Using your acid demand test drop your pH to 7.0 and not any lower. Either pour the measured amount of acid SLOWLY into the return stream and away from the skimmer or mix the acid into a large bucket of water and "walk" it around the pool. Predissolve dry acid in a bucket of water and "walk" it around the pool if you use it instead of muriatic.


3. Test your TA (at first it will not move much, if at all!)

4. Begin aerating and do not stop until the process is complete and TA is where you want it (if this is possible).

5. Monitor pH and when i climbs above 7.4 do another acid demand test and add enough acid to drop the pH to 7.0 again.

6. Test TA again. If TA is still too high keep aerating until pH is above 7.4, dropping pH to 7.0, and testing TA. Be sure to do an acid demand test each time because THE AMOUNT OF ACID YOU WILL NEED TO DROP THE pH TO 7.0 WILL DECREASE AS THE TA DECREASES AND THE SPEED AT WHICH THE TA DECREASES WILL INCREASE AS THE TA DECREASES! Do not try and cut corners by not testing every time or using the same amount of acid every time! If you do you will run the risk of dropping the pH well below 7.0 and potentially causing damage to pool surfaces or equipment!

7. When you TA test indicates that your TA is exactly where you want it to be then just aerate the water until is is between 7.4 and 7.6 and you are done!

The process is actually easier than it reads once you start doing it so don't be afraid of it. This is the ONLY way to safely and effectively lower TA in a pool or spa. Don't get discouraged if nothing seems to be happening at first. You will soon seen the TA start to drop as you continue the process. Also realize that as the TA drops the process speeds up and you will need less and less acid to drop the pH to 7.0 and each drop to 7.0 seems to 'eat up' the TA faster.

Good luck!smile.gif

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  • 4 weeks later...

I will give this one a try, How about dropping a sump pump with no hose in the pool? Maybe a Sta-Rite 2hp? That should aerate things a bit. Might have to Tie a large stone onto it though.

It sounds like you're being facetious, but using a pump, such as a pool cover pump, will just move the water around and won't pull in air. However, some people have used air compressors attaching a pipe with small holes to create many small bubbles and that aerates a lot (obviously just putting the pipe end into the deep end of the pool -- leaving the compressor outside the pool). Most people just do something with their returns -- just pointing them upward and running the pump on high will churn the water surface. Some people add aeration devices to their returns.

picture of an aerator

pictures of another aerator

If one has waterfalls, spillovers, fountains, etc. then running those will help to aerate the water. In my own pool, I've just pointed returns upwards and though this does speed things up, it's not as effective as something that involves a greater amount of air-water surface area.

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I will give this one a try, How about dropping a sump pump with no hose in the pool? Maybe a Sta-Rite 2hp? That should aerate things a bit. Might have to Tie a large stone onto it though.

It sounds like you're being facetious, but using a pump, such as a pool cover pump, will just move the water around and won't pull in air.

I am going to assume you are being serious and give you the benefit of the doubt. (Thanks Richard!wink.gif)

IF it can shoot a stream of water up into the air and then back into the pool it should work. I have used home made return fountains made from PVC successfully. After the 90 deg fitting I have a foot long section ((approx) of pipe with an endcap glued on and sever slits cut into it with a hacksaw. One or two of those in the return can aerate a pool very effectively suing it's own filtration system. If you need to lower TA on a route then perhaps the best way is to just drop the pH to 7.0 (love those acid demand tests!) when you service the pool. When you return in a week the pH will have gone back up from outgassing of CO2 since the lower the pH the faster it will outgas and pH of 7.0 (which will start to rise in about a day) the pool is still swimmable. Test the TA and do another acid demand and add more acid, repeat until one day you come back and the TA is on target, normally a few weeks to a month of weekly visits (for cal hypo that means between 80-100 ppm and for a SWGC 70-80 ppm). If you then maintain the pH between 7.6-7.8 you should find that your pH is more stable for a longer period of time (assuming we are not talking about a new pool with curing plaster)

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  • 2 weeks later...

awesome. i'm going to try this today. i have to add tons of hose water every single day to one of my commercial pools, and so i'm going to just put a nozzle on the hose and fire it into the water instead of letting putting the end of the hose into the water like i normally do. firing it into the water will create the turbulence and pull air down simultaneously! i'm excited to have a new technique that i've never heard anyone local discuss!!!

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awesome. i'm going to try this today. i have to add tons of hose water every single day to one of my commercial pools, and so i'm going to just put a nozzle on the hose and fire it into the water instead of letting putting the end of the hose into the water like i normally do.

My concern here is what is the TA and pH of the fill water? If it is high then you need to be also dropping the pH to 7.2 when you fill. Does this pool have a leak somewhere or is this a normal water loss? Have you done a bucket test to check for leaks? If the pool is leaking then maintaining proper water balance becomes a challage since you are disrupting all your chemical levels as you add fresh water to the pool daily.

firing it into the water will create the turbulence and pull air down simultaneously! i'm excited to have a new technique that i've never heard anyone local discuss!!!

If it is a large pool this probably will not create enough aeration to cause significant pH rise quickly. Lowering TA is a process and (having cared for commercial pools myself) one that is normally not fast enough to keep the pool open the whole time. My recommendation for a commercial pool that must remain open is to lower pH to lowest acceptable limit by using your acid dmand test (if you lower it to 7.0 at night when the pool closes it should be up to 7.2 by morning. If you can set up some type of aeration overnight so much the better), turn off any acid feeders overnight, but keep the pool circulating so you have some pH rise during the night. Test pH and TA in the morning before opening and drop pH back to 7.2 if it has risen above 7.4 overnight. pH will rise more during the day as the water is aerated by the bathers so make sure you turn your acid pump or CO2 back on if used. At closing check pH and TA and repeat again. It is a bit slower than the continuous acid addition to keep pH at 7.0 and continuous aeration to outgas CO2 but the advantage is that the pool does not need to be closed for a day or so to complete the process and your water parameters stay within swimmable range.

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  • 1 year later...

Welcome Birdman15!

If your pH is stable, then you don't need to lower the TA, at least not for that reason. If your chlorine is low and you are starting to get cloudy water, then that might be algae growth starting and you should shock the pool. If your pH, TA and CH are all on the high side, then your cloudiness could be due to that, but I suspect it's algae from the too low FC level. The appropriate FC is based on your CYA level. See the The PoolSolutions Best Guess Swimming Pool Chlorine Chart.

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  • 3 months later...
  • 5 years later...

We have a 3700 gallon vinyl pool.  Our TA is at 280 and pH is 7.8. I want to try this method... it makes sense to me.

 I have two questions ...

Our Phosphates are at 500 right now, should I do a PhosFree treatment first?

Should I try to keep the Chlorine at the normal swimming level during the process of lowering the TA?? or should I raise it up the Shock level for this treatment?


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