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Constant Ph Drift Up


GtownDan

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The CH won't affect your pH. A higher TA has more carbon dioxide outgassing and causes the pH to rise unless you are using net-acidic sources of disinfectant/oxidizer. That's a chemical fact. The dealer is wrong about low TA -- their concern is that you are using a net-acidic disinfectant and this uses up the TA and has the pH get too low, which can then cause metal corrosion in your heater. You say you had corrosion issues with your heater in the past, but was this with too low a pH? It shouldn't have corroded if the pH got too high, but if the pH/TA/CH are high, then scaling can occur and that can damage (burn out) the heater.

The lithium hypochlorite you are using is like any hypochlorite source of chlorine that is fairly net pH neutral. So the rise in pH you are seeing is due to the TA that is too high. By lowering the TA to 50 ppm, you minimize the associated carbon dioxide outgassing. TA is a measure of the over-carbonation of the water. I suggest you use 50 ppm Borates after you get your TA lowered since that will help to stabilize the pH and be a substitute pH buffer to compensate for the lower TA.

By the way, lithium hypochorite is VERY expensive. Also, how did you get your CYA level to 30 ppm? Did you initially use Dichlor to build it up? If you don't start out with some CYA in the water, then the chlorine is too strong and that can lead to earlier corrosion as well and be harsh on swimsuits, skin and hair. You might consider using the Dichlor-then-bleach method though you can use up the lithium hypochlorite in place of the bleach since you've already purchased it.

So to reiterate, it is low pH, not low TA, that can cause metal corrosion. Low TA will not harm the heater elements nor the acrylic surfaces -- it is low pH that can do that. High pH, if with high TA and/or CH, can cause scaling and that can cause heater failure as well, though not from corroding but from scaling the heat exchanger causing heat to no longer be transferred so burning up the elements (raising the temp in the heater too much). There is a misunderstanding that a low saturation index causes corrosion, but it just causes calcium carbonate to dissolve from plaster -- your spa does not have plaster nor grout in tile so no calcium carbonate to dissolve.

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Thank you for the reply and clarity, it’s a great help. My CYA is high, according to my dealer, because of a cleaner I used in the tub to rid of a thick grease type stain they occurred above the waterline on initial fill and before the tub was used. One employee recommended the cleaner; however after using it, another told me it was not a good idea. TDS now at 1,200 and CYA is at 40 as a result.

I don’t mind using the lithium for now as opposed to bleach. I think I’ll continue on this path for the moment.

My PH now seems to have stabilized at about 7.5 however I do have some light scaling in the tub (fine sandy feeling on walls and seats that easily rubs off). I assume this is due to too high Calcium Hardness (CH) approx. 220. I need to drain my tub this weekend to bring down my TDS (before the really cold / freezing weather sets in – Canada), I anticipate this will also bring down my CH. When I refill I think I’ll aim start out with the following and see if I can keep my PH stabilized around 7.5: CH: 150; Al: 80; PH 7.5; and, CYA 40.

Thanks again for your invaluable input.

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A CYA of 40 ppm is not high.  It's about right.  You want at least some CYA in the water if you are using chlorine (which you are).

Yes, your scaling could be from the somewhat higher CH along with TA and pH.  Though you could lower the CH by partial water replacement, you could also just lower the TA level and in that process you would lower the pH at least temporarily so that would help to dissolve the scale (if that's what it is).  For your next refill, if the pH tends to rise, lower the TA.  80 ppm might still be too high, but it depends on the amount of aeration in your spa.  If you need to get to 50 ppm TA, then consider adding 50 ppm borates as well. As for CH, 120-150 ppm is usually enough to prevent foaming and is low enough to prevent scaling if your other water parameters are OK (especially if your TA is lower).

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  • 6 years later...

I also have the issue of constant high pH and low TA. I use monopersulfate and Nature 2 to kill bacteria. I have never had the issue with TA and pH until recently and I've had the same spa for over 20 years. My question - can a faulty ozonator or heater cause the pH to increase? I set and check calcium hardness regularly but it's never an issue. I've tried draining and refilling a few times and within a couple of hours the pH is shooting up. I've tested my tap water and it's always very good with the pH about 7.6 or so. 

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