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

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I think you need to take a step back, get a good test kit and post the full set of water parameters (FC, CC, pH, TA, CH, CYA, Salt, Temperature). Then we can work from there.
 
Awesome.

Firstly, I'll try to change from the CTX-15 (14.5% SA) to a proper Muriatic Acid (hopefully at the 31.5% range or even higher if exists). Let's see if the cheaper option brings any obvious conclusions (I'd like to be a brand's fault, but this is the second brand I use and the problem remained, so...)
After that, if things remain as they are right now, I'll buy the product you suggested and get the parameters checked.

Thanks for your help, I'll keep this post updated.
 
Hi once again,

Just a quick update:

Yesterday I went to my local bricolage shop and bought just 1L of Muriatic Acid (30% Hydrochloric acid). Unfortunately they ran out for now of those 5L bottles.
I checked the PoolMath app and it said I would require 1.3L to drop from 8.0 to 7.0, with TA of 80 for a 65 000L pool.
Today I diluted that 1L of MA into 10L of water and spread the mix around the pool, the bigger part over the 4 return jets I have. Surprisingly, after 3h of circulation, my pH dropped from 8.1 to 7.6. I'll say it again: 0.5 pH with just 1L (and still reducing, I believe)!!! It's crazy!

There are only two explanations for this (that I can think of):

1) The CTX-15 is not doing its job (but I tested in a smaller sampler (15L of well water to 0.2L of acid, checked the pH and it was way below 6.8 after 1h or so)
2) My water has much more single ions (I'm no chemical engineer, sorry for my ignorance or mistake in terms) to be found by the target acid, therefore it works best with MA (H) instead of SA (H2).

Thanks everybody once again for pointing MA as the best solution, indeed it is working far better than any product I used before and using a much smaller quantity.
 
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ThatPoolNewbie said:
diluted that 1L of MA into 10L of water and spread the mix around the pool
Click to expand...
No reason to do that. Increases risk of spilling by double handling the acid. Just pour the acid slowly at a pool return with the pump running. Brush the area if you like to insure mixing.
ThatPoolNewbie said:
Surprisingly, after 3h of circulation, my pH dropped from 8.1 to 7.6. I'll say it again: 0.5 pH with just 1L (and still reducing, I believe)!!! It's crazy!
Click to expand...
The acid rapidly disperses and the pH drop is instant, so after 30 minutes, you will see the full effect if your pump is running.
 
I just diluted because every video I saw on YouTube advised me to. But sure, since I'm already dropping the acid over pool water, diluting is of no much use.
I left my pool pump running, but in circulation instead of filtering. I didn't know if it could damage the sand of my sand-filter, so I didn't want to do any harm to it.
Since 5h now have passed and it remains at 7.6, I believe I'll need another liter to get it to that sweet spot of 7.3 I personally like. But, of course, it will be harder to maintain there rather than at 7.6. But, since MA turns out to be much more effective than SA, I feel I'll start spending less product so I think I'm able to do it less frequently.

I believe the SA is correctly labeled. At least, I downloaded the the datasheet from their website and it says the same: 1.2L for 0.2 pH drop on a 100 000L (concentrated) or 3.25L for the same reduction on the same pool size (diluted).

www.ctxprofessional.com

CTX-15 pH-

www.ctxprofessional.com

After the batch of tests I was able to do (everything I've described throughout this post), I'm more inclined to say that I have some type of metal that binds better with a single H ion (MA) rather than 2 (SA).
That would explain why its effectiveness had reduced over time, perhaps some type of saturation has been reached and now the SA can't find no more any set of two ions to bind to that easily.

It's just a guess, as I said I'm not a chemist or anything alike. Mostly likely I'm saying a total non-sense.
 
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This TA of 80 is from a test strip, right? I think you really should get a proper Taylor K-2006. Have a look at the link I posted. I suspect that your TA is actually much higher than you think it is. That will explain why you see a smaller change in pH to start with, and also why it rises so quickly again.
 

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You're right, I see it (TA) using test strips from AquaChek

Analisador de água - Jardim | Leroy Merlin

Adquira Analisador de água aquachek cloro/ph na Leroy Merlin. Consulte aqui todas as informações disponíveis.
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It gives me a green tone, that is exactly the one from 80 ppm range (I refilled the pool last Friday, so I guess it went up a little bit since last measure).
Most probably you're right, perhaps its higher than what the strip shows.
 
FWIW, My AquaChek test strips showed my TA around 50-80. It was in reality actually over 200 when testing with TF-PRO *and* verifying that 200+ number with my pH meter (4..5 pH during the test is at the color change). So those AquaChek strips aren't accurate for me with TA (they're close with FC and pH though).
 
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Dang, it was a complete shot away from the target, perhaps its happening the same here.

Yesterday I've bought 25L of MA and I'll start to use them in the pool, when needed (around 0.5/1L to set the pH from 7.8 to 7.3/7.4/7.5 and then use the rest with the acid pump, when it becomes higher than 7.6). Let's see if the pH increase rate drops, same with the TA and acid consumption). Thanks for your input.

PS: Definitely I would require a better test kit as suggested previously, but I'd like to use it only as a last resort measure. Unfortunately It is a little bit expensive for our reality (Portugal).

But if in a short-medium term the MA solves it...right? I'll keep you guys updated.
 
Quick update:

I added 1.4L of MA directly into the pool and the pH dropped from 7.9 to 7.2/7.3 right away (within 5 mins). Now the math (from PoolMath) is indeed correct.
But I believe as pointed out that the TA might be higher that what is shown by the test strips since it should have taken a little bit less to do the same as expected (if it was TA 80).

I've already set the acid pump to not let the pH rise above 7.5, adding MA drop by drop.
Do you guys believe for TA purposes it is the same doing drop by drop with the acid pump rather than doing it manually with a bigger amount at one go? Time is not a concern for me, I guess.

But sure, I've much better results now. As I said, with sulphuric acid I used to drop lately around 12L of acid just to see a drop of 0.1 pH...It was unbearable.

Can't thank enough every single one who supported this post, it seems I can finally rest my head around this subject that has been haunting me for months.
 
Hey guys,

Seven months have gone by and ,"boy let me tell you", MA was the best idea you guys could have came up with.
I started buying MA (30%) to fill the bottle of 25L and it took me 2 months at first to use 80% of it. Very, very good improvement against what I was experiencing on my first post.

During the summer and start of autumn, don't know if still due to high temperatures or relatively "normal" TA (perhaps higher than what I said it was), often I saw the pump running for a few seconds every day to maintain the pH within the limits (7.3-7.4).

Now, with no refilling from the well - it has not rained for a long time but the temperature is low and occurs little evaporation - the pH has been at 7.1 for like a month.
And it is reading well 'cause I also used the Test Kit and the value matched.
The TA surely is lower than before and is helping to keep the desired value.
Also turned off the SWG (not advised by the supplier to work on temperatures below 15 ºC otherwise can cause premature degradation) and started using chlorine tablets during winter. That definitely helped a lot!

Everything is smooth now.
The only thing I found not that great is that the rubbers of my pH pump and the tube from where the MA is sucked from the bottle started to suffer some effects: the tube became completely white and the ruber inside the pump that makes the bridge between the incoming and outcoming started to become brown, inclusively with some metals (rollers) inside to start a reaction that turned some small parts to a blue-ish green.

The company that sold and installed all the pool items had to come to my home to replace the clock that triggers the start and end of the pool's daily routine and I asked about it. The guy just told me that it must have been done because of the MA, that the pH pump was meant to be used with ph- and not MA. Fair enough. I was spending 150€ every week, now I spend 25€ every 6 months (autumn/winter/spring time). Even if current material (rubbers and tubes) are not fit for MA usage (at least of 30%), if anything broke with all the savings I've been making I could still buy a new one or pour it myself manually (the only thing that is indeed helpful is the reading, not the auto-injection drop by drop).

Anyways, just wanted to update you guys and thank you again so very much. It was a huge relief I had finally fixing this problem that tormented me for almost one year (head and money-wise).

Cheers!
 
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