spa thermai blanket and pH, will blanket control pH?

[jwfrank]

i recently decided to replace my hot tub cover, and in so doing, came across the idea of using a termal blanket (closed cell polyethelene foam, supposedly clorine resistent - but after receiving it I have to wonder if one needs to pay the premium for this from a spa store ??)

My goal was to protect the new spa cover's underside from chlorine vapor and to retain the water's heat better

I have noticed after a few days that my pH DROPPED from 7.9 to 7.4 and has remained constant. At first I thought it may have been beacuse of a chemical reaction between the spa water and the foam. But now I am wondering if the termal blanket has an effect on the outgassing caused by the spa's jets which come on (with some air bubbles) during the filtering/heating cycles. The blanket seems to trap below it all the gasses and vapor

Before the thermal blanket. I had to add muriatic acid every 3 or 4 days to lower pH even though I do not ever use the heavy duty jets, just those low pressure jets that circulate/hest the water for 2 hours , 3 times/day

TA is 50, and borates 40-50

So my question is: might the thermal blanket be a very effective tool to moderate , reduce, or eliminate pH rise due to the natural aeration of spa water? If so, this is for me a BIG advantage

 

[chem geek]

It sure does sound like the extra blanket is inhibiting carbon dioxide outgassing and therefore making the pH more stable. I'm a bit surprised that a regular spa cover doesn't help enough, but I suppose the gaps in the cover seal at the edges of the spa isn't as good as when you use the blanket that provides another barrier to water-air transfer.

 

[jwfrank]

thanks, Richard. I was hoping you would see the post and weigh in with your always-welcome advice.

Does it make sense to you that preventing outgassing of carbon dioxide might actually REDUCE pH, not just keep it stable?

To help stem pH increasing before the blanket, I had been keeping TA low @50. Now with pH @ 7.4, that gives a CSI of -.74. Do you suggest that I allow TA to rise to 80 as long as pH stays in 7.4 -7.6 range???? (CSI would be -.5 or -.32)

It will be interesting to see if the blanket keeps the pH stable even with the above-mentioned increase in TA

 

[chem geek]

If there were no outgassing, the pH would be stable. So if it dropped, something acidic happened in the spa. Don't forget that chlorine usage is acidic so the pH will drop a little as chlorine gets used up and will go back up when you add a hypochlorite source of chlorine.

The low CSI doesn't matter if you have no plaster surfaces or grout in between tile to protect.

 

[jwfrank]

Thanks, Richard