Difficulty keeping pH down

[8tracklover]

Hi all,

I'm having trouble keeping the pH at a good level in my swim spa. I've had the spa about 6 months. I'm using the standard TFP approach: 10% bleach, dry acid to lower pH, baking soda to increase alkalinity, and borates to try and limit pH fluctuations.

I'm adding about 7 oz. of dry acid (or equivalent muriatic acid) every other day to bring the pH down to 7.4.

I suspect one of two things, but would appreciate other's advice and experiences:

1. Natural use of the spa raises pH due to any lotions, creams, or other chemicals bathers may have on their skin or hair. Though, I've heard that bathers actually decrease pH. Not sure, though.

2. The mineral filter is causing it. The mineral filter is Masterspa's ecopur filter, which releases zinc and copper (I think).

Here are this morning's measurements:
FC: 2.5
TC: 0
TA: 100
pH: 8.0
CH: 160
CYA: <30
Borates: 30
Current water temp: 95 F

Thanks.

 

[8tracklover]

Ok so right after I posted my question, I stumbled on the pinned post that talks about spa water chemistry basics. I think it answers my questions.

Here is the blurb that pretty much sums up what's going on in my spa:

"However, pH will have a tendency to rise with aeration (i.e. use of jets and air), more so if your TA is high. Although, as long as you're not adding Acid (or anything with a lower pH) to your tub, the pH will not usually drop. Therefore, in hot tubs the problem is normally pH rise (or Drift), because of all the aeration. So, the trick is to get the TA high enough to not create an unstable situation, and low enough to not allow pH to rise too much."

The recommendation is to keep the TA at 50. My TA is set at 100(!). And my jets are pretty much always set to aerate. I'll follow the advice given in the post and report back with m,y results.

 

[Nigel459]

I believe you are on the right track. It's normal for pH to rise when your TA is higher (I think due to off-gassing of CO2). Until my TA gets down to around 60 my pH will rise with aeration.

Edit: yep, you found it

 

[Divin Dave]

Man I have some fond memories of my old 8 track players back in the 70's. Cool user name!

Good job on finding the answer to your rising pH.

 

[abycat]

i find any spa i run needs a ta of 40 to be very stable. all the pools seem to like 50 ta.