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PH Alkalinity Issues


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Hi all,

We have 500 gal hot tub and have had it for about a year now.  I have yet to be able to get PH and alkalinity into spec at the same time - as a result I have focused on PH.

I have yet to find anyone locally who can help with this issue.

If Ph is in spec, say about 7.6, my alkalinity will be about 20ppm.  If I bring ALK into spec, say 100, my PH is north of 8.6. When I bring my PH back down (PH down/sodium bisulate), ALK goes too low. 

When I raise ALK, I am using Sodium Hydrogen Carbonate (baking soda) which I have read is supposed to move PH minimally - in my tub, it moves PH up a lot.

I have had my ColorQ system verified by a local shop so I know it is not my tester giving me false readings.  For example, the sample I brought to them yesterday, had PH at 8.1 with ALK at 47ppm.  I followed their recommendation to bring both in spec(ph down and ALK up), I tested this morning and had a PH of 7.7 and ALK of 25.

Has anyone had this issue?  Ideas?

Thank you



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Hey Rich,

The wisdom on this forum tells us to set the TA to a point that provides the target pH. In my case, 70 ppm TA will give me about a 7.6 pH.  A TA of 20ppm does seem really low and I would expect your pH is very vulnerable to sudden drops with the addition of anything acidic.

I suggest that you post a full set of test results, what sanitation system you are using and anything else you maybe adding to the water.  One of the forum experts, like @waterbear might be able to give you some guidance once he has the additional information.

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  • 2 weeks later...

I'm right there with you guys.  My pH and alkalinity are only in spec when the hot tub is first filled.  Heating and aeration raise my pH to over 8.  Knocking the pH down with acid just drops the alkalinity.  I'm tired of chasing both pH and alkalinity and as a result just drain and refill my hot tub every few weeks.  I need to know which is more important pH or alkalinity? My understanding of chemistry is the alkalinity gives the water the buffering capacity to resist changes in pH.  


Any insights are appreciated!

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Dont be too focused on "range chemistry."  A stable ph that is between 7.2 and 8 is what you are looking for.  If your TA needs to be at 50 ppm to put you into this pH range, then so be it.  Just keep you eye on the pH.  If you ph is too high, go ahead an lower both TA and pH with acid and then aerate to bring the pH up in the proper range.

I keep my TA at 60ppm on the dichlor then bleach method so my pH will not have such a great tendency to rise up past 8.  

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New here to the forum.  I was looking for help with settings on my hottub, but saw this thread and thought I'd jump in to see.  I've had my hottub for quite a while.  I am the only one that uses it. Being averse to chemicals, I use Essential oils---Geranium.  I sprinkle 15 drops (400 gallons) and never have any problems with my water.  I read about this method years ago and have used it with consistent results.  I have on occasion dropped in some "Thieves Oil" also. No rashes, no foam, no scum, no chemistry out of whack.  I don't know why but it works for me.  Just putting that out there.  Super easy/cheap!

Hope you all have a relaxing day!

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