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.
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Larry
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Reduce Total Alkalinity Levels

Postby Larry » Mon 16 Jan, 2006 16:24

The acid slug method in this post has been discussed and disproved throughout this thread. Here is a safer and better method for reducing Total Alkalinity written by Richard aka chem geek. Quoted in this post for easy reference.

The following method assumes 6.8 is the lowest measurement on your pH test kit:

StepAction to TakepHTANotes
1Add AcidlowerslowersAdd enough acid to bring pH down to 7.0
2AerationraisesnoneAerate until pH rises to 7.2
3Add AcidlowerslowersAdd acid to bring pH down to 7.0 (continue to aerate)
4
Aeration & Acid
nonelowersRepeat steps 1 & 2 until TA reaches the target
then AFTER you have reached your target TA
5AerationraisesnoneAerate until pH rises to your target (say, 7.5)
Net resultnonelowers


chem geek wrote: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


This was the classic method, now debunked:

Here is a step by step guide to reduce the Total Alk of swimming pool water:
  1. Turn off the pump and wait at least half an hour for the pool water to stop moving.
  2. Choose an open spot in the deep end of the pool and pour the required amount of pH reducer slowly into this one spot. If you are using granule or powder pH reducer, first dissolve it in a bucket of water.
  3. The water will become hazy (like the heat coming off a hot road) and may bubble. This is normal.
  4. Allow the pH reducer to do its work for 20 - 30 minutes, then turn on the pump and circulate the water for at least 4-6 hours.
  5. Test again after 48 hours and repeat as necessary.
To find out how much pH reducer you need, you can use these handy Total Alkalinity Calculators. The calculators are metric and the conversions are:
1 gallon = 3.8 litres
1kg = 2.2 pounds
1 litre = 34 ounces

After giving the pool an "acid shock" like this, it is usual for the pH to drop. The high Total Alk causes the pH to rise again naturally, so wait several days after correcting the TA before adjusting the pH up. It is usually not necessary after the wait.

There are some who suggest that this method can harm some pool surfaces and they warn not to add more than 2.5 pounds of pH reducer for 10,000 gallons of pool water every 3-4 days. I regularly use up to 20 pounds for 10,000 gallons in one go and I have yet to have a problem. As long as the hardness level is at least 200ppm there is no reason for problems.

Comments and suggestions are welcome.
Larry


Ted

reducing total alkalinity

Postby Ted » Wed 12 Apr, 2006 20:18

Larry, thank you for the guide to reduce alkalinity. Pulled back the cover on our pool this evening and very surprised to see crystal clear water. I closed the pool last October knowing TA was extremely elevated. The water has not filtered yet but 'pre tested' tonight and found pH at 7.4 and TA at 260ppm. I have a 28,000 gallon, in ground, vinyl lined pool. Using your TA calculator, the recommended dosage was almost 17,000 mL or by my conversion 35lbs of acid.

In my past experience, it has been very, very difficult to adjust TA. Should I plan to reduce it using your guide? My other idea was pump out some water and refill with fresh to dilute the TA?

Can I get your initial thoughts? Will begin filtering tomorrow, planning to open in 1 month.

Thanks.
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Reduce total alkalinity

Postby Larry » Thu 13 Apr, 2006 03:57

Hi Ted

High TA with normal pH is not a critical problem. If you maintain your pH slightly lower, at 7.0 - 7.2 for example, you can offset the effects of the high alkalinity in the pool water.

I recommend that you keep the pH stable, and when it goes up use the above method to reduce the alkalinity and the pH at the same time. Adding vast quantities of pH reducer to a pool with normal pH will result in low pH, which is more detrimental than high alkalinity.

Replacing water will not make any difference if the TA of the fill water is too high (I assume it is as you mention that it has been very, very difficult to adjust TA). Adding fresh water increases the chemical demand of the pool water so it costs you money in chemicals as well as water and I do not advise this.

Seeing as your pool water is "crystal clear", try to avoid excessive additions of chemicals which may unbalance the apparently good water.
Ted

TA

Postby Ted » Thu 13 Apr, 2006 17:11

Larry, thanks for the advice. Great website!!!!!!!!!!!!!
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Re: Reduce Total Alkalinity Levels

Postby oasis » Fri 02 Jun, 2006 05:00

Larry wrote:Here is a step by step guide to reduce the Total Alk of swimming pool water:
  1. Turn off the pump and wait at least half an hour for the pool water to stop moving.
  2. Choose an open spot in the deep end of the pool and pour the required amount of pH reducer slowly into this one spot. If you are using granule or powder pH reducer, first dissolve it in a bucket of water.
  3. The water will become hazy (like the heat coming off a hot road) and may bubble. This is normal.
  4. Allow the pH reducer to do its work for 20 - 30 minutes, then turn on the pump and circulate the water for at least 4-6 hours.
  5. Test again after 48 hours and repeat as necessary.
To find out how much pH reducer you need, you can use these handy Total Alkalinity Calculators. The calculators are metric and the conversions are:
1 gallon = 3.8 litres
1kg = 2.2 pounds
1 litre = 34 ounces

After giving the pool an "acid shock" like this, it is usual for the pH to drop. The high Total Alk causes the pH to rise again naturally, so wait several days after correcting the TA before adjusting the pH up. It is usually not necessary after the wait.

There are some who suggest that this method can harm some pool surfaces and they warn not to add more than 2.5 pounds of pH reducer for 10,000 gallons of pool water every 3-4 days. I regularly use up to 20 pounds for 10,000 gallons in one go and I have yet to have a problem. As long as the hardness level is at least 200ppm there is no reason for problems.

Comments and suggestions are welcome.
Larry


Hi lary,
I have been using muriatic acid to reduce pH.
whick acid is better? sulphuric, nitric, or phosphoric acid?
jane

high alk and can't get the chlorine to go up

Postby jane » Wed 12 Jul, 2006 20:32

Help!! I could deal with the cloudy water for a few days but it keeps saying 0 chlorine after we have dumped and dumped chemicals. What can we do?
Don

Alkalinity

Postby Don » Tue 29 Aug, 2006 06:36

Larry

I understand you should "plug" with acid to lower alkalinity. But can you explain how the plug works as opposed to acid dribble around the pool?What really happens in the process.

Thanks Don
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Re: Alkalinity

Postby me » Tue 29 Aug, 2006 08:38

Don wrote:Larry

I understand you should "plug" with acid to lower alkalinity. But can you explain how the plug works as opposed to acid dribble around the pool?What really happens in the process.

Thanks Don


It's the concentration of the acid at the specific spot that is supposed to "break" the TA by liberating carbon dioxide. A bit like dribbling vinegar on baking soda. You'll get more of a reaction (you'll get more bubbles) if you pour the vinegar in a single spot as opposed to spraying it around.

By spreading the acid around the pool, a process known as "walking the acid", the concentration is not enough to "break through" the TA (and a high enough TA will be able to absorb such a pH swing).

Opinions vary as to the effectiveness of this method though. Another method is to lower the pH of the water and create turbulence, or aerate the water, in order to liberate carbon dioxide.
Iain

Very high TA and pH

Postby Iain » Sat 18 Nov, 2006 15:08

I look after a 10-11,000 gallon pool for my parents.

In summer 2005 we drained and refilled so as to repair some small damage to the vinyl liner and to jet down and remove some scale.

TA has always been an issue - it's a very hard water area - and since the refill keeping TA and pH down has been a nightmare. The scale problem seems to be getting worse. The water itself is remarkably clear despite low chlorine, but 'knock down' algae from algicide sticks to the liner...I presume due to scale. So you can have clean water but a dark green liner and vac-ing only makes it less green, it doesn't clean it, I presume as the algae is sticking in the scale.

The algae can be so bad as to foce me to vac to waste (unless I want pea-green water after the first few mins of vac-ing) which of course makes matters worse as I then need to top-up...with fresh hard water.

Currently TA is around 250ppm and pH 8.0. My thought is to 'acid shock' using HCl which will chlorinate, reduce TA and drop the pH all in one shot. I am loathed to use hypo chlorine as that only adds to the alkaline load.

Does this sound a sensible approach? I calculate around 13 litres of 30% HCl to get me from a TA of 250 to nearer 80ppm. That should also drop the pH significantly which I am keen to do in the belief (correct me if I'm wrong) that a deliberately low pH will help dissolve the scale. So really I am thinking of deliberately dropping the pH down to help remove the scale. Once that lifts then to push back up to the 7.2 level.

So I'm all open to suggestions. These are just my thoughts, but some sound advice would be gratefully received :-)

Many thanks.../Iain
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Reduce Total Alkalinity Levels

Postby aliencam » Sun 03 Dec, 2006 14:25

i have never heard of this being called "plugging" but have always referred to it as "slugging", i guess the same thing.

In layman's terms (this is how i explain it to customers,) when you pour the acid in one place without the pump circulating, it is more concentrated. This way it can just stay in that one area being more concentrated and "burn off" all of the carbonates (alkalinity is more of less the measure of carbonates in water), which escape through the top of the pool as gas (which is the bubbles you will see.) The reason it doesn't lower the pH as much when you turn it on an (hour) later, is because most of the strength of the acid is "used up" by the time the pump comes on.

When lowering alkalinity, i space it out, as too much acid in this process, or leaving it too long, will end up destroying the pool's surface. here are the doses I prescribe:

maximum amount added per day:

10,000 gallons=====32 oz. Muriatic Acid=====16 oz on either side of the deepest area of pool one hour before the pump runs for __ days (to reach the amount of acid required to lower alkalinity)

15,000 gallons=====48 oz Muriatic Acid=====24 oz on either side of the deepest area of pool 1 hour before pump runs for __ days (to reach the amount of acid needed to lower alkalinity)

i use proportions of that dose for all pools.
under 5,000 gallons, i would not suggest muriatic acid, but instead dry acid
if pool depth is less than 5 ft, i would suggest a lower dose
NEVER do this is any pool that is not concrete/gunite/pebbletek(pebble sheen, pebble whatever)

it is easiest if you add the acid one hour before the pump comes on automatically, people have a tenancy to forget how long it has been.

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