Hot Tub fresh fill - City Water 50ppm & 7.8pH

[Terv]

Hello,

I recently used Ahh-Some, flushed and refilled my hot tub.

City water to start:
TA 50ppm
CA 50ppm
pH 7.8

I build a bromide bank to 30ppm with liquid sodium bromide and use a floater with BCDMH pucks to sanitize.

After one month:

TA 50ppm
B 30-50ppm - Gentle Spa (it is hard tell exactly using Borate test strips)
CA 130ppm
pH 8

How do I lower the pH to 7.6 and maintain or get the TA to 50-60ppm?


Thank you,

 

[pooldv]

Just lower the pH to 7.8 and it won't lower the TA much. But, if you need to raise TA use baking soda and it won't raise your pH.

More here about chems and what they do, Pool School - Recommended Pool Chemicals

 

[Terv]

Hi Pooldv,

Thank you for the quick reply.

Yes, I have been doing that but the TA drifts down the pH drifts up so I end up TA 40ppm and pH 7.8-8.0.

It turns out there is an air injection system factory built into my hot tub. It runs 24 hours per day in tandem with the filtration system. The manufacturer includes the aeration in all hot tubs to allow for the option of an ozonator. I do not have or use an ozonator. The manufacturer has advised if I plug the air intake there will be no more air injection on filtration. Filtration will continue to run 24 hours per day.

I suspect the BCDMH bromine pucks sligthly increase the pH and I am wondering if the 24 hour aeration is slightly lowering the TA.

I do not know if all hot tubs have aeration and if it serves some other purpose but I am thinking about plugging the air intake so there is no more air injection.

Does this sound prudent?

Thank you,


PS: Anyone else is welcome to reply.

 

[MPurcell]

BCDMH is acidic, so it will reduce pH and TA, not increase it. MPS is also slightly acidic, and will reduce pH and TA. Bleach is approximately pH neutral. However, aeration will increase the pH without affecting TA, and aeration running all the time would be a problem, I think, as the pH would go high rather quickly.

 

[pooldv]

Aeration raises pH which causes you to add acid to lower PH which then lowers TA. My filter cycle only runs one hour per 12 hour cycle. There shouldn't be a need to run the filter 24x7. Is that adjustable to run less? My tub has a valve to open and close the air so it is off most of the time. It also puts a lot of cold air into the water dp when it is cold outside and cools the tub.

But, there is nothing wrong with letting TA drop to 40 and adding baking soda to raise it back to 50.

 

[Terv]

Hello MPurcell and Pooldv,

Thank you for the replies.

I have a Hydropool hot tub and the aeration jet is separate from the pressurized self cleaning filtration system. The aeration jet sends a steady stream of fine champagne like bubbles into the hot tub 24/7. If the optional ozonator is installed, they connect the ozone venturi line to the aeration line to introduce ozone into the hot tub. The only filtration option is on 24 hours or off. I am not too concerned about the filtration system running 24/7. When using the hot tub there is an adjustable valve from 1 - 5 to control the amount of air that is injected via the massage jets.

My question is about the aeration jet that injects a steady stream of champagne like bubbles from the bottom of the hot tub. Since I do not have an ozonator I can see no reason to inject bubbles into the hot tub 24/7. Unless there is some other function, which I am not aware of, it seems to me the benefit of disabling the aeration jet will be a reduction in pH drift. As you indicated above that is what I have been experiencing. The pH is rising to 8 and I add dry acid to bring it back down to 7.6 which lowers my TA to 40. I then add baking soda to raise the TA back to 50. And I now suspect the independent aeration jet is the culpret that raises the pH back up toward 8, creating an endless cycle that only adds more stuff to the water.

Unless someone advises another function the aeration jet performs, I will disable the aeration jet supply line and post my results back in a couple of days. If I am correct, with CA 130, TA 50 and Gentle Spa (borates) 50, I should see more stable pH around 7.6. It may even decline with the BCDMH bromine pucks. I do not use MPS. I found 12% sodium hypochlorite (chlorine) to be more manageable. I add 1oz after every use. It raises the bromine above 10ppm and by the next evening it is back down in the 2-4ppm range. Chlorine makes sense to me because that is the C in the BCDMH bromine pucks. The less stuff I introduce into the hot tub the better.

Thank you for all of your help!

 

[MPurcell]

I agree that adding chlorine as an oxidizer makes more sense than using MPS. I use BCDMH in a floater, and 8.25% bleach to oxidize. In my tub, pH and TA both tend to diminish over time, and I wind up using baking soda to raise the pH and the TA. Yesterday my pH was down to 7.0 and my TA was at 70. I added 7 Tablespoons of baking soda, and after pH was 7.7 and TA 120. Today my pH is 7.6 and TA is 110. I have the floater set to keep the bromine level the same if there is no use, and only add enough oxidizer to offset the bather waste when we soak. Tubs are different though, and yours may not react like mine does.

I really don't know about tub design, but if you can eliminate the aeration, I think it would be a plus for you. I'd just make sure you're not going to cause any problems with the equipment.