No matter how much acid, my PH won't lower except my TA.

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Pool Guy 75
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No matter how much acid, my PH won't lower except my TA.

Postby Pool Guy 75 » Sun 20 Jul, 2008 15:47

I've been experimenting with my 12,000 gallon pool lately to find out how to adjust my TA to its ideal range, as well as my free chlorine, CYA, etc. I've been a wiz at this for some time and jotted down mathematical equations I've came up with to maintain my pool every now and then.

The probelm starts here: My PH in my pool is supposed to lower naturally as it always rains every now and then, organic matter builds up, people swim in my pool,etc. At the end of the month I test my pool's PH, free chlorine, TA, CYA, etc. The results are quite often the same (TA= 50-100 ppm, CYA=ideal, Free Chlorine= 0.5 to 3 ppm, PH= 7.8-8.4). Now, after shocking, backwashing, and cleaning my pool I have to add between 0.5-1 gallons of liquid chlorine in order to maintain my free chlorine levels between 1ppm and 10 ppm ( I do this twice a week). Everytime I add chlorine to the pool no matter how much, The free chlorine rises to 10 ppm, but the amount that I add regularly makes the free chlorine last for 2-3 days (on the 3rd day it lowers to an ideal range). Basically it seems easy to super-chlorinate anytime I want with only one jug of liquid chlorine for an entire week. After, adding chlorine my PH tends to spike upwards as high as 10.5 and doesn't lower even after adding acid for more than 4 days (not adding chlorine anymore).

The only time I ever see my PH go down is when I only maintain my pool for atleast a month with Algaecides, Phosphate Removal products, and shocking weekly with DuraShock (contains DiChlor).

Some experts have told me that I should dilute the acid I'm using into a bucket of water and broadcast it evenly around the pool, because if too much of the acid concentration is added to one area of the pool, then the PH in that area will quickly lower to 5.5 and below, and the Alkaline minerals,etc. in the pool will react with the acid and neutralize it. Thus, the TA will be lowered and most of the acid will cancel out, causing little or no change to the PH in the Pool.


BTW, the amount of acid I put is based on the Aquachek calculators for PH and TA in the Aquachek website. It tells me that I should put 16 oz of acid to balance the PH when I add the amount of chlorine that I previously mentioned above (basically it's the free chlorine present in the pool). If the PH is already past its maximum it tells me that I should add about 20-32 oz of acid to lower it from a PH of 8 and above to a PH of 7.6.

Does anyone have any other advice that can help with my problem?


chem geek
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Postby chem geek » Mon 21 Jul, 2008 13:00

The standard phenol red pH test is not valid above 10 ppm FC making the pH seem higher than it really is. Shocking with a hypochlorite source of chlorine does make the pH rise, but it drops back down when the FC drops. Any net rise in pH is due to carbon dioxide outgassing but at a lower TA level that won't happen. The fact that your measurements are ranges seems to indicate that you are using test strips and they are not accurate. Get yourself a good test kit, the Taylor K-2006 kit at a good online price here or the TF100 test kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so is comparably priced "per test".

With Dichlor, for every 10 ppm FC that it adds, it also increases CYA by 9 ppm. You generally do NOT want to shock with it unless your CYA is low and you intentionally want to raise it.

You can use The Pool Calculator for calculating dosages and can learn more about maintaining your pool by looking at The Pool School .

Richard
Pool Guy 75
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Postby Pool Guy 75 » Mon 21 Jul, 2008 13:21

I haven't put any chlorine since Friday, and now that my free chlorine levels are low (less than 1 ppm) I diluted 20 oz of muriatic acid in 6 gallons of water using the recommended 1:10 ratio (actually 6 gallons is enough, just wanted to be extra careful). So, this morning I added that much of the diluted acid into my pool, and waited for 8 hours to pass.Then, I tested my pool's PH and it shows that it's in the 7.8-8.4 range, but not as high as when I have more than 2 ppm of free chlorine in the pool. After, I added again more acid, but only 12 oz of it dliuted in 4 gallons of water.

Is muriatic acid weak or something, because I tested the PH in the bucket water containing the acid and it shows that it's in the 6.8 to 7.0 range? That doesn't seem enough to lower the PH in pool, either I have to add 20 times the amount of acid applied times the amount of water in the bucket (basically 20 more buckets of water+acid), or I have to lower the TA enough so that all the Sodium Bicarbonate in my pool is gone, which will make my ph lower alot quicker and at that moment I can add borate as a PH buffer to stabilize my PH more efficiently than with the sodium bicarbonate in my pool, which increases my PH when added.

Any suggestions?
chem geek
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Postby chem geek » Mon 21 Jul, 2008 21:15

If you dilute some acid in a bucket as you are doing and only measure it as 6.8 to 7.0, then there is something wrong either with your pH test or with your acid. Muriatic Acid is normally 31.45% Hydrochloric acid which has a pH of -1. A 10:1 dilution would have the pH be 0. It should be at the extreme of the lowest pH your test can possibly do. Even half-strength Muriatic Acid that is around 15% is still about the same pH.

I suggest you get a good test kit as I had indicated. If you are using test strips, I wouldn't trust them.
Pool Guy 75
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Postby Pool Guy 75 » Tue 22 Jul, 2008 00:06

can aeriation actually cause PH to rise constantly? like the water jets in my pool which shoots water out in a river-flood fashion (kinda like the water jets in a hot tube but the water drained half way).


If this is a factor, should I change the angle of the jets to shoot out less water over the waters surface level?

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