Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.


Postby ash123 » Fri 18 Jan, 2008 13:33

I work at a hot tub store and we have a customer with some serious water issues. These are his readings and what i am trying to figure out is how his ph could be so low to take the finish off of his head rests and gold jewelry. So here is his readings

Bromine 2.00
PH -6.5 :?
Hardness 0.0
Alkalinity 0.0

He (the customer) said he does not use ph reducer and the only chemical he buys is bromine and shock. PLEASE Help me get him some answers. He has drained and refilled and his water is fine now but he still wants answers and i dont blame him.[/b]

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Postby mr_clean » Fri 18 Jan, 2008 14:20

The pH value of bromine is 4.0, which like chlorine tablets is very acidic so using some PH up will help them raise their level. Bromine use needs to be monitored normally 2-3 times a week.
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Postby chem geek » Fri 18 Jan, 2008 14:21

If the shock is non-chlorine shock, potassium monopersulfate (MPS), then this is acidic though not strongly so (it's a strong acid, but the quantities are usually not large). The jets in a hot tub will outgas carbon dioxide causing the pH to rise (with no change in TA) so the MPS will have both the pH and TA drop -- the net result being a lowering in TA. Eventually, as the TA gets lower and lower, the pH will drop more and more from the MPS until eventually the TA gets so low that even a small amount of MPS wil lower the pH quite a bit.

If one starts with a pH of 7.5 and TA of 100, then adding one tablespoon of MPS evey day would reduce the pH to 7.3 after a week. After one month, it would get down to 7.0 and the TA dropped to 90. After two months, the pH would be 6.7 and the TA 80. I suspect that more MPS than I describe may have been added or there may have been another source of acidity. mr_clean points out that bromine tabs are acidic -- not as much as Trichlor, but acidic nevertheless -- so that probably contributed as well (though my calculations show it's not a huge factor -- BCDMH isn't as strong an acid as CYA -- but combined with MPS usage the two together could be a large amount of acidity over time).

Basically, if one doesn't monitor a hot tub at all, then the chemistry can get out of balance. In this case, some baking soda (or Alkalinity Up) should be added immediately. Not too much, however, as you don't need to get too high, but getting to around 80 or more would be good in this case (if the customer isn't going to monitor their tub regularly, then play it safer and get to 120 ppm TA). Then the customer needs to periodically, at least weekly, check their TA level and add more as needed. If the pH is low as well, then pH Up / Spa Up (Arm & Hammer Washing Soda) can be used and this will raise both pH and TA.


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