Ph levels

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Ph levels

Postby BigF » Fri 25 Apr, 2008 08:48

A Scotsman with his first pool! The upside of living in south of Spain. The down side .... all the gear - no idea!

Our pool had to be emptied to be descaled as the last owners had not looked after it properly. Job done, now been refilled for a month and water now seems fantastic - bright and clear.

Have chlorine at (DPD) 1.0 mg/l and stable - adding 4 - 6 tabs at a time till gone and then replacing (these are 5in1 tabs). However I cannot get the Ph (phenol red) to lower it's at 8.2. I beleive it should be at 7.2

I have added alot of acid + but to no avail. The water here is very hard and i am worried that without enough acid - the calcium scale will return.
Do I just add more?

My tester is a simple tablet test and only measures pH and Cl. What is total alkalinity and how do you test?

What else in needed?

Pool is 27,000 ltrs

Looking forward to being a bit more educated. Thanks for assistance.


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Postby chem geek » Fri 25 Apr, 2008 11:38

Most 5in1 chlorine tabs are Trichlor which is very acidic so it is very strange that your pH is so high if that's the case. So first of all, look at the ingredients on your chlorine tabs and see if it says something like "trichloro-s-triazinetrione" or "trichloroisocyanuric acid". Another possibility is that they are Cal-Hypo tablets so see if it says something like "calcium hypochlorite".

If your pH wants to rise a lot, then it's likely that your Total Alkalinity (TA) is very high. Along with a high Calcium Hardness (CH) and higher pH, that would have led to calcium carbonate scaling. You need to get yourself a good test kit -- the best is the Taylor K-2006 but I don't know if you can get that in Spain. Instead, see if you can find a test kit with the following tests:

FAS-DPD chlorine test (hard to find, but a better test than OTO or DPD)
Total Alkalinity (TA)
Calcium Hardness (CH) (not Total Hardness)
Cyanuric Acid (CYA)

If the TA is indeed high, then you lower it by the aeration at low pH with acid addition approach described in this post. Are you using Muriatic Acid (31.45% Hydrochloric Acid) or dry acid (sodium bisulfate)?

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Postby BigFergo » Sat 26 Apr, 2008 03:48

HI Richard.

Thanks for your speedy reply.

Just to make things more complicated - the 5in1 tabs are trichloroisocyanuric acid (90-93%) [disinfects, algecide, flucculant, anti-lime & ph.

"a complete treatment for pools with very hard, problematic water or prolonged absence"

I will try to get a better test kit as described.

As far as acid is concerned - have used a granular acid yellow in colour but no longer have the tub, and liquide acid no longer have the container - so i guess is one of each.

I'll try to confirm today.



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