Help with TA and pH balance

[port 13]

Split by moderator from HERE. jblizzle

im struggling! I used the above instructions. filled the hot tub, added calcium to get the hardness to 130, then added borax and acid to get borate level to 50. next added baking sode to get the TA to 130 (based on pool calculator), then added acid added to get the pH right. then "shocked" with chlorine to 10 ppm. though everything was great, but rechecked and TA was down to 40 due to amount of acid i had to use to get the pH right. just added more baking soda (only half the amount to get the TA back up) and the pH is is back over 8. what am i doing wrong, it doesnt seem like i can get to a TA of 130 AND have a pH of 7.5. . . . please help!

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

I'm sorry your struggling with this. Hang in there, you've almost got it.

You are correct that you can't easily have a high TA and a low pH when there is aeration in a spa. Why are you trying to do that? The instructions say to target a low TA, such as 80 ppm, not 130 ppm. If the saturation index is too low, then you compensate for that by targeting a slightly higher pH, say 7.7, and/or increasing the Calcium Hardness (CH) level somewhat. However, having a somewhat negative saturation index in a spa is not a problem as I assume you don't have plaster/gunite/grout exposed to the water.

A higher TA will result in a faster rise in pH. You don't need to keep your TA so high. Get your TA lower, leave it there and don't worry about it being lower, and let the pH drift up a bit and don't try to lower it much below 7.7 or 7.6. You don't have to try and keep it at 7.5. You should find a point at lower TA and somewhat higher pH where the rate of pH rise slows down significantly.

By any chance, do you have an ozonator?

Richard

 

[port 13]

Re: How do I use Chlorine in my Spa (or pool)?

no ozonator. i was using the TA that got my saturation index at zero. thanks for the help, i'll make the adjustments.

 

[port 13]

Re: How do I use Chlorine in my Spa (or pool)?

I'm still having the same problems. I am now using a goal TA of 80, but still can't get there. I seem to have stability with a TA of 40 and pH of 7.6 (will stay like this days on end without any chemicals). If I try to raise the TA higher, then the pH goes with it. I have used nearly an entire bottle of dry acid trying to zero in on the "perfect" numbers. Am I safe at a TA of 40 (saturation index is at -0.6, but don't have plaster or stone)? Do you have any other suggestions?

I really do appreciate the help, I feel like I am so close. . .

port

 

[chem geek]

Re: How do I use Chlorine in my Spa (or pool)?

So long as you don't use any acidic sources of chemicals, such as Dichlor (or Trichlor) or non-chlorine shock (MPS) and you are very careful with adding acid, then a lower TA is OK. See if you can get to a TA of 50 ppm with a pH of say 7.7. That would be a tad better with a little more buffer "just in case". There are some other spa users that are in the 50-60 ppm range and I think one was around 40 so what you are experiencing is not unusual. It's just additional proof of how a higher TA leads to a faster rise in pH and that the use of bleach is actually pH neutral.

The other thing you could do is use 50 ppm Borates in the water, but that probably won't lower the amount of acid you have to add over time, but it will make such acid addition less frequent and slows down the rate of pH rise. Also, I'd recommend the Borates if you plan to keep your TA very low because it will help reduce the amount of pH rise that occurs immediately after adding bleach (it drops back down as the chlorine gets used up).

Do you have pretty substantial jets or other sources of aeration? Do you keep the spa covered when not in use (I would assume you do)? Are you using Clorox Regular unscented 6% bleach or are you using another brand?

Richard