Can't keep my pH at the optimal range (7.4-7.6)

[ThatPoolNewbie]

Hey guys,

My first post in this forum and I'd like to appreciate any further comments/suggestions in advance.

I have a concrete pool with almost one year old (SWG). The concrete is not in direct contact with the water, it has a impermeable "skin" all around that is used as a finish and cover of the sides and bottom. I didn't know anything about pools but now I think that I'm pretty aware of many things that could unbalance my pool but not this one. I fill my pool with a well water, that may have a significant amount of copper in it since the by the two times I put salt into it then it became green (right after a few minutes) for a couple of days until it got back to its beautiful blue. I believe its copper since I got some yellow stains around the water-line, that I was able to remove.

During the winter, I didn't get much attention to it, I admit. I thought it was pretty easy to handle (just check the machines, ensure water was clean, etc...) but then came the spring, small little pieces of algae started to show and I started to study how to get rid of those issues. I installed an acid pump, that allowed me to be more sure of the pH level.

My pH was around 8.2 (or a little more), because the natural ceiling is around 8.4/8.5 and hadn't had any maintenance from my side until that point.
I bought several amounts of ph minus (25kgs each) and started to let the pump do its work. It took a long, long time to drop it until 7.2, and to drop the alkalinity from 240 ppm to 70/80 ppm. To speed things up, I did it manually pouring huge ammounts at once around the pool and being previously diluted.

I'm very concern with this because I just have the return jets (15/20 cms below the water line pointing horizontally) and somehow my pH rises around 0.1 each day (if the acid pump is off). I think its too much when the jets don't even create bubbles, just a slight turbulence. I've tried to keep it around 7.2, 7.4, 7.6 and now 7.8, but its hard to keep it in between any of those values (harder on the low end) without wasting and wasting bottles of acid (around 25 kgs in 1 week, if not less).

Since I live in Portugal, we don't have your usual pool stores. Even the strips have much less info that yours (only TA, pH and FC). Things got worse when I started adding chlorine tablets to a dispenser when I was one week away and had no salt to relay on the SWG, and when I added granular chlorine to fight the greenish tone of my pool when I put the salt back in it a week later.
Since then, the pH is around 7.8 (wasting almost a bottle every three days).

May it be due to high calcium hardness? I don't know its value, but I guess the chlorine tablets and granular might have messed it up. I dropped huge amounts of acid and it seems to have no result lowering the ph now...it's weird but that's the truth. It just "maintains" it at 7.8.

This has been giving me headaches for months, I just wanted to understand what may be happening so I can fix it accordingly. I can't afford to waste that much of acid (and money) that fast.

TA: 70
pH: 7.8 (and rising)
FC: 2.8

65K liters / 17.2K gallons concrete pool with impermeable "skin"
SWG + Acid pump + Sand filter
Filled and refilled with well water (around 2000L every 3 weeks or so on spring/summer season, no need to refill on autumn or winter)
All equipments run the same number of hours as the water pump (8)

Cheers!

 

[Texas Splash]

Welcome to TFP! So I'll give you some things to consider that might help:
- Here in the US, wells generally have iron not copper. If you see a stain and can remove it with a Vitamin C tablet (citric acid), it's iron. If you can remove the stain with dry acid, its copper.
- We see metals react less when the FC and pH are well controlled. But salt pools generally like a higher pH due to aeration. For you to force the pH lower would require a lower TA and consistent use or acid.
- Your TA can probably go as low as 50, but no more. For acid, see if you can find muriatic (liquid) acid versus the pH minus that contains sulfates. Sulfates build-up and are no good for our pools.
- Calcium isn't much of an issue with the exception of protecting the plaster in your pool.
- A good test kit is extremely important. Test strips, even ours in the US, are junk. Maybe see if you can get a Taylor K-2006C ordered online and sent to you there. That would be ideal.
- We balance our FC to the current CYA of our water per the FC/CYA Levels to avoid algae.

Hope some of this helps.

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[mknauss]

Welcome to the forum!
I suspect your water has iron in it. Stains from copper are very hard to remove. Iron just takes some ascorbic acid.
How much fill water do you add to your pool? I suspect that is what pushes your pH higher.
CH does not make your pool green nor is it added from stabilized chlorine tablets. Scale is the main effect from CH being high.
You are in a bad spot on testing. Some folks in the EU use MYUS.com to ship test kits to them from the USA.
I suggest you read ABC's of Pool Water Chemistry.

 

[ThatPoolNewbie]

Thanks guys for your replies.

Let me try to answer your questions:

The aeration was considered. Because of that, I had my SWG turned off for around 2 weeks to see the impact of it on that matter and, unfortunately, it was none. The pH just kept rising 0.1 every day.
I'd like to try to get the TA down to around 60 or 50 as you suggested, but since almost 25 kgs were not enough (somehow) to drop it a single tenth, I'd like firstly to understand what is the real explanation rather that keep wasting it without results or just hoping for the best. Every bottle costs around 30 dollars, too much for our reality.
The pH minus I bought is around 34% sulphuric acid, and supposedly requires 1.2L to drop 0.2 pH on a 100 000 liters pool. Mine is 65 000 liters and with the remaining 10L from one bottle it did nothing. Something is preventing the acid to do its job, I guess. That or that bottle in particular was sold with pure water in it (I'm joking).

The yellow stains were not completely removed. The most of it was, but with a good eye you can still see some tone of yellow on the water line mostly due to sun exposure. The ones I cleaned previous to that exposure, I was able to clear properly. I'm just assuming it's copper because of the reaction (blue to light green) but yes, might also be iron.

I refill with 2000/3000 liters every 3 weeks or so due to natural evaporation and some wind. My concern is more within those 3 weeks when I used to get ph back to 7.4 but it started to rise upwards after it.
Since I used those chlorine tablets 2 weeks ago, the pump just keeps pouring acid but the pH does not drop. Just keeps at 7.8 and wasting 25 kgs every 3 days...it's too much for any wallet. Before that, the acid did its job (decent rate of reduction) but yes, the water just kept rising its pH back then at a lower rate but significantly high too.

I do not have any waterfalls, most of the time I don't use the pool, so the only thing that could make CO2 being released was water circulation. At least the ones I could think of, obviously. But since it makes no bubbles, just a small turbulence that pushes the water towards the skimmers...my educated guess was to ignore that slight movement.

I fall asleep and wake up thinking in this subject and I would really appreciate any idea that could guide to the real "evil". I believe I'll find the answer in this great forum.

Thanks in advance!

 

[Texas Splash]

Given your additional info, I would try to find muriatic acid. Use the MA to try and lower the TA a bit more. To do that though, be sure to let the pH get to about 8.0 before using enough MA to lower the pH to 7.0. That larger swing/adjustment "should" have much better impact on the TA. With the TA 10-20 ppm lower, it may help to slow the rise of pH. I suspect your well water also brings to it not only metals, but also an elevated TA which would explain why acid is continuously required. If we assume (or you confirm) you do indeed have iron versus copper, you might try circulating pool water through some polyfill material which can sometimes help capture the iron. You can see examples on YouTube. If tends to capture more iron when the iron has precipitated outwards in the water, but it can help lower the iron level.

 

[ThatPoolNewbie]

Thanks again for your further investigation alongside.

Two more details to help:

1) The water from my well (its not a well, more likely a borehole water where the pump is 150 meters below the surface)...once I tried to see how is the pH directly from the source (using a pH kit) and it gave me around 8.2 pH. Also, it has very high TA - around 240 ppm.

2) I was wrong when I gave you that percentage of sulphuric acid. I checked the label of the last statement I bought (6 bottles) and those have only 14%. I've been told that the brand I use to buy from (CTX-15) had a case where a particular burned his skin severely due to lack of knowledge on how to deal/handle acid. So they started to sell a "diluted" version since then, only allowing the concentrated version to be sold to professionals. Once I re-checked the label, I understood that the one that was sold to me was the diluted version. Maybe that's why I don't see the same rate of lowering pH as I was used to (34% (before) vs 14% (now)).

You guess that Muriatic Acid (31%) will do a better job than sulphuric acid (14%)? Although SA has a lower concentration, it has a bigger ability to nullify alkalines. If so, I'll buy a bottle just to try out.

 

[Texas Splash]

Yes, we see wells in the US with much higher TA levels. Some areas of the county have a TA close to 500 ppm!

We also have low % (low fume) muriatic acid in the states. But the 31.5% is still available. Sometimes they are is different sections of the hardware store (pool, paint, etc). But if you only have the 14% that certainly explains why you have struggled to attain the targets you were looking for. Not sure if you know about this already, but our PoolMath APP (Effects of Adding) can help you with dosage amounts as well.

 

[mknauss]

Sulphuric Acid leaves sulfates in your pool water. Sulfates build up and will damage the Salt Water Chlorine Generator, any other metals in your water, and concrete. So be ware of using sulphuric acid.

 

[ThatPoolNewbie]

Thank you for your input, it surely helps me.

I'll try to find a good Muriatic Acid in my local bricolage store, I think I've seen one a few days ago while passing by. And I'll be aware from now on of that side-effect of sulphuric acid that I didn't know about.
I'll lower the pool's TA until 50 and see if that can slow down the pH increase rate. I really can't understand why with such a low TA (70) it increases that much in a singular day (0.1) for a pH of 7.8, but let's hope that with 50 it can stabilize more.

I've also requested a more extensive pack of strips (6 in 1) that can give me and you guys more details on the major parameters.
I'll post the results in few weeks time, when it arrives.

Thanks once again to both of you.

 

[mgtfp]

Although SA has a lower concentration, it has a bigger ability to nullify alkalines.

That is not the case. The TA reduction is determined by the increased H₃O⁺ concentration when lowering the pH. It doesn't matter how you decrease the pH, whether it's muriatic acid or sulphuric acid. If the amounts of acid result in the same pH- change, then the TA-change will also be identical.

In the US, sulphuric acid typically comes with a concentration of about 38.5%. The required amounts to achieve the same reduction in pH and TA are very similar to the required amounts of 31.5% muriatic acid.

When using 14% sulphuric acid you'll need more than double the amount of 31.5% muriatic acid to achieve the same effect.

But as mentioned already, sulphuric acid has unwanted side effects. If available, then stick to muriatic acid.

 

[ThatPoolNewbie]

Thanks for your reply.
Just wondering...can you explain me what is the "low fume" around Muriatic Acid? Is it preferable than the 31.5% if there are any differences? And why? Just to know what to buy within the MA range of products.
Thanks in advance

 

[mgtfp]

Low fume muriatic acid usually just means lower strength muriatic acid. But sometimes they also sell mixtures of muriatic and sulphuric acid as low fume acid. Do make sure that it really is just dilluted hydrochloric acid (aka muriatic acid) when buying low fume acid.

Low fume doesn't mean that it's better quality, it's just less concentrated (or contains sulphuric acid).

Muriatic acid is actually not very dangerous. The fumes smell nasty, but the smell actually protects you from taking a deep breath. Just make sure the wind blows the fumes away from you, not towards you. If you are really not comfortable with the fumes, then use half strength muriatic acid - I personally don't see a point in paying basically double the price and having to schlepp double the volume/weight home.

But you need to protect your eyes, splashes into the eye can create damage, always wear eye protection. And always add acid to water. Never add water to acid.

Splashes of muriatic acid on your skin are not dangerous as long as you wash it off straight away - you have a pool full of water around you. Splashes of sulphuric acid on the skin are actually more dangerous, even though it doesn't appear as harmful because it doesn't fume.

No matter which type of acid you are using, avoid splashes on brick, mortar or concrete. Or metal. And don't wear your best suit when handling acid.

And don't store acid in a closed room, the fumes are quite corrosive. I store my acid in a plastic tub with a lid, outside, protected from direct sun, and out of the way from kids.

 

[ThatPoolNewbie]

Thanks again for you reply. Very useful and detailed info.

I have an acid pump, I was not thinking in using it manually all over the pool. Just thinking in let the bottle right next the water pump and let the acid pump do its work. Just a small hole on the cap so the plastic tub can be dig in to provide decent suction.

One thing is bothering me:

I installed the PoolMath app and was making a few experiences. I imagined the worst case scenario I had with my pool (TA: 240, pH: 8.2) and targetted a 7.2 pH. It calculated it would need just 3 liters of MA on a 65K liters pool. I guess it is too little for the purpose. if I recall correctly it took me around 75 liters (3 full bottlles) to have the same result the first time I did it, with a 38.5% sulphuric acid concentration (yesterday I wrote 34% but it is indeed 38.5% like in the US).

May it be a liter conversion "bug" or you guys in the US have had results with such a low use of MA (converting to gallons, obviously)?

 

[mgtfp]

I installed the PoolMath app and was making a few experiences. I imagined the worst case scenario I had with my pool (TA: 240, pH: 8.2) and targetted a 7.2 pH. It calculated it would need just 3 liters of MA on a 65K liters pool. I guess it is too little for the purpose. if I recall correctly it took me around 75 liters (3 full bottlles) to have the same result the first time I did it, with a 38.5% sulphuric acid concentration (yesterday I wrote 34% but it is indeed 38.5% like in the US).

I assume, you mean 7.5 liters? Are you sure that wasn't 15% MA? That would be about right then.

 

[ThatPoolNewbie]

No, no...I really mean 75 L (3 bottles of 25 kgs / 55.12 lbs). Ok, since acid is more dense than water (1kg = 1L) it won't be precisely 75 L, but almost it. It took me 3 full bottles to get it back to 7.0/7.2.

If 3 liters took everything back to normal than I wouldn't be wasting so many bootles of acid (since each one has 25 kgs, it would take a long, long run to get empty). Or the calculations are wrong or I have something on my pool that is preventing the acid to be as performant as it should be.

I used 3 bottles of 38.5% SA (CTX-15 "concentrated"), the label said 1.2L to lower 0.2 pH on a 100 000L pool.
Now I'm using bottles of 14.5% SA (CTX-15 "diluted"), the label says 3.25L to lower 0.2 on a 100 000L pool.

Either way, it is taking me much, much more acid that what the labels said/say. I didn't add borates or something like that to the water (that I'm aware), so why would the acid take such huge amounts to get a proper job done when pool math and the labels say otherwise? At my area, well/borehole waters tend to be very hard. Do you think that might be the reason?

 

[ThatPoolNewbie]

Hi guys, thank you in advance for any help you can provide me.

Despite other issues I addressed in a previous post, I'm more concerned right now to understand one in particular.

To lower my pool's pH (around 8.4/8.5 pH with a TA of 240+), it took me 3 entire bottles of pH Minus (CTX-15) that were around 38.5% sulphuric acid.
It took me almost 75 kgs (!) - yes, 75, not 7.5 - to drop the pH to 7.0 and the TA to 70 ppm.

Nowadays, I'm using a "diluted" version (14.5%) of the same product, since some client had severe burns due to bad usage of the product and the concentrated one is only sold to professionals.

Right now, my acid pump just keeps pouring acid and there's practically no benefit from it. I can waste a full bottle (25 kgs) and just notice a 0.2 pH reduction overall, if I'm lucky.
If the pump is off, my pool rises around 0.1 pH every one day or two on its own with simple return jets 15/20 cms below the water line and pointing horizontally. No bubbles show up, just a slight turbulence that pushes the water towards the skimmers. No waterfalls, and the pool is barely used by me or any family member.

These are the infos at the labels of those CTX-15 products:

Concentrated: 1.2L to lower 0.2 pH on a 100 000 L pool -> (around 6/7 L expected vs 75 L used)
Diluted: 3.25L to lower 0.2 pH on a 100 000 L pool -> (around 16.5 L expected vs ... in use)

Either way, the labels do not reflect my experience. I almost waste 1 bottle every 3 days (it's unbearable to any wallet - each bottle costs around 25€).
By what is said, it should be much more performant to keep the pH at 7.8 with TA of 70, at least. And I can't even drop that value using the acid pump, it kinda remains there but with the acid being dropped into pool.

I guess there must be something extremely unbalanced in the pool anywhere to turn the acid's performance that bad, I guess. But I really don't know what. Since the strips here in Europe have just a few info's (FC, pH and TA), I can't really tell you anymore than that. It is believed that the well water I use to refill may be very hard (don't know if it gives you any clue).

Can anyone share any suggestions?

Thanks

 

[mgtfp]

Over which period of time for you add the acid? Was that a longer period? In this case, aeration would have worked against the acid, and therefore it took longer until pH dropped down to where you wanted it

 

[ThatPoolNewbie]

Around 1-2 days when done manually and using the 38.5% SA solution. Doing it using the acid pump took around 4-5 days.

The problem is that aeration, imo, should be neglected. The return jets don't create bubbles, just a small turbulence and are significantly below the water line. If that explained 0.1 every day I guess it would be uncontrollable for those pool owners with waterfalls and that make intense usage of their pools (dives, ...).

I still feel that must be something within the water, some parameter that must be preventing the acid from being fully performant. But it is just my guess, I'm no professional or pool expert. :/

Thanks again for your help.

 

[mgtfp]

So, the time does seem to play a role. You saw a more noticeable effect on pH when adding the 38% SA within 1-2 days, compared to adding the 14.4% SA over 4-5 days.

How did you get that value of 240ppm for your fill water TA? And if you didn't pay much attention to pH/TA until recently, the pool's TA might be significantly higher than the fill water TA. Evaporation removes pure water (low TA) from the pool that you replace with high-TA fill water, so TA keeps building up over time. In hot climates (i.e. high evaporation) with low rain fall, TA keeps building up in a pool, especially when the fill water's TA is high.

The dosage recommendations on those bottles are very oversimplified. For example, the amount of acid needed to reduce pH from 8.2. to 8.0 is about 3 times smaller than the amount needed to reduce pH from 7.2 to 7.0 - the pH scale is a logarithmic scale to start with.

When using Chem Geek's PoolEquations spreadsheet with TA 240ppm, I get 4.1L of 38.5% SA required for a pH-reduction from 8.2 to 7.2, with 14.5% SA it takes about 12.7L.

I could imagine that your TA is actually larger than 240ppm, and due to the high TA, CO2 outgassing happens very quickly.

If above amounts of acid are added over a longer period of time, you will not see pH drop that quickly. But to get TA down, that doesn't really matter. The TA reduction is proportional to the amount of added acid. If added quickly, pH and TA will drop quickly, and pH will then rise again due to outgassing. If added slowly, TA will drop slowly, but the pH-drop might get compensated "on the fly" by aeration, so the full effect on pH is not visible. But once the full amount of acid has been added, the drop in TA will be the same as when added quickly (unless you also topped up with fill water in the meantime).

75L of 14.5% SA would have brought your TA from 240 down to about 50.

Before you keep adding these amounts of acids, you need to be sure about your water parameters.

I know it's difficult to get good test kits in Europe, but you need a Taylor K-2006 or something comparable, those test strips are pretty useless. At least for CH and TA you could use aquarium test kits if nothing else is available. For TA you might need sodium thiosulfate chlorine remover drops as well, like Taylor R-0007, depending on the indicator that kit is using, as indicators can get bleached out by chlorine.

A member from Spain successfully got a Taylor test kit from here:

Analizar Agua: Tienda online de analtítica

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That page was down for a while for maintenance, but it seems to be working again.

Are you using CYA (cyanuric acid, aka stabilizer, sun-block, conditioner)? If not (or not enough), then your SWG is probably producing large amounts of chlorine per day to keep up with chlorine decay by UV. It can theoretically happen that some of the chlorine gas that's been produced by the SWG doesn't dissolve in the water, but gets lost. This would create an additional rise in pH and TA, on-top of the pH-rise by aeration (which doesn't affect TA).

 

[ThatPoolNewbie]

Once again, I can't really thank you enough for your time and knowledge.

My TA is now around 70 ppm. It has become stable since a month ago (when I decided to be a proper pool owner and set every thing I could to its optimal level), but even with a low value (from 240 to 70 using those 75 liters of acid), my pH keeps rising everyday, obviously now at a lower rate but high enough to be 0.1 pH every single day or two.

Today I opened another bottle of 14.5% SA, of 25 kgs. By the time the pump shut down (18:00, 40 minutes ago), it already took around 1/4 of the bootle (6.25 L). It started with 7.9, dropped to 7.8. Too much acid for too low results.

I haven't add anything but those chlorine tablets two weeks ago when I had my vacations. Coincidently, it was the time when I started using those "diluted" bottles of SA. Before that, I had the "concentrated" version of the product. Despite the rising on pH still existed, it was way less consuming on the acid perspective. For you to get a wider picture, I used to waste a bottle every week, keeping my pH at 7.4/7.5.

Once I added the chlorine tabs and changed to the "diluted" version, I just can "maintain" the pH, it's much, much harder to lower it even a single tenth. Only after I came back I was able to refill the missing salt and restarted using the SWG. I believe the pool guy that installed it didn't now much around the subject since I believe its undersized (it is designed for a 60K liters pool and my pool is around 65K). I only run it at 40% (he told me not to "stress" it since it would reduce its lifetime and 40% would be enough), so I guess my chlorine is not that high (2.6/2.8 ppm at this moment). I don't know if this is important (perhaps it is), but when I refilled the salt my water became light green due to presence of metals within the water. To fight that back, I added lots of granular chlorine that rose the FC until 10 ppm and only a few days ago I put my SWG to work again (when below the 3 ppm).

I did get the 240 ppm readings using my strips directly from a sample of water, not from the pool but from the hose. The upper limit is 240 ppm on my strips, could have been higher for this sample. But since the color matches, I supposed that this was its value.