Increase TA spikes my pH

[Scott20165]

I have been struggling with this problem for awhile.  All my reading this subject hasn't helped.  

360 gallon hot tub.     

My TA drops so I tried to raise it.   I'm using SpaGuard Spa Total Alkalinity.    Every time I attempt to raise the TA, my pH spikes.   Then I'm following up with several cycles of pH decreaser.   A cycle being putting a small amount of pH decreaser in, running jets for 20 minutes then checking.    Because my TA has increased, the pH is slow to come down.  

The basic question is, why does my pH spike when I increase TA?

 

Thanks,
Scott

 

[MPurcell]

The ingredient listed for SpaGuard Total Alkalinity Increaser is Sodium Hydrogen Carbonate 100%. This is just another chemical name for Sodium Bicarbonate, or simple baking soda. Chemical formula is NaHCO3. This is the product always used to increase alkalinity, but it also increases pH, which is why your pH spikes. Incidentally, you can save yourself some money by buying Arm and Hammer baking soda when you run out of the TA Increaser.

The benefit of having a higher alkalinity is to stabilize pH. You didn't say if you are using chlorine or bromine as a sanitizer, but if you are using bromine tabs in a floater, they are slightly acidic and will bring the pH and total alkalinity down. Also, if you use non-chlorine shock to oxidize bather waste (MPS) it will also bring the pH and total alkalinity down. I have found that in my spa, the pH tends to drift down over time, and this causes the total alkalinity to also decrease over time. So I use sodium bicarbonate to raise the pH, but I target the pH and not the total alkalinity. So, if I push the pH up to 7.8 with sodium bicarbonate which increases the TA as well, then the pH tends to drift down more slowly.

On the other hand, if you find your pH rising, then you want to have a lower total alkalinity. The usual recommendation for a spa is a TA in the range of 50 to 80. I currently have TA about 110 in my spa, and the pH still tends to drift down slowly because of the bromine tabs in the floater.

[Scott20165]

MPurcell,

Thanks much for the excellent advice.   Perhaps I'm trying to push my TA up to high when it's not needed.    

I was using bromine but recently empty the tub, changed the filters, filled, drained and filled again to get a fresh start.    I'm now trying the Zodiac W20750 Nature2 SPA Stick Mineral Sanitizer.    I'm hoping to have better luck or at least more knowledgable on water chemistry.

Thanks again,

Scott