Ph Goes Up, Alk Down

[farwellbooth]

Hello,

I realize PH and Alkalinity are often issues and I've read a lot here, and elsewhere. After 3 years of hot tub ownership I'm still struggling with these two. Ph always goes up to a higher more basic number. I use a Taylor kit and it's often at 8.0, a dark purple. Alkalinity also creeps down. Here is my equipment, numbers and chemicals I use:

-Caldera Cantabria spa with ozonator. About 615 gallons

-I use Leisure time chemicals: bromine tabs, clarifier, renew and spa up. I shock every couple weeks with about 3/4 bleach. After bathing I add 1 renew tab per person. There are just two of us and not a ton of tub traffic. I use the clarifier about every two weeks.

-The Taylor numbers are typical Can++ 180, Ph 8.0 (this always goes more basic), Alk 60 ish (this always creeps down), and bromine 3-5 ppm. The water is always very clear. I'm in Seattle and fill with city water, change about 2x/year.

From what I read I adjust the Alk first. Most literature says over 80 however I've taken the advice here that 50 is ok. Regardless, once the Alk is in range I use and acid to get the Ph back down. I've tried both muratic acid and bromic. Both work however the Alk also comes down. If I start with the Alk higher, say 80, I can get the Ph at say 7.6 and Alk at 50 of which is fine. The problem is then a couple days later the Ph is back up to 8.0 and the Alk slowly creeps down, say 40 if I were at 50 when things were in line. So I'm constantly adding Spa Up to get the Alk at a good starting point, then acid.

I have a blower and waterfalls of which with the jets make a lot of bubbles. I run these in attempt to make the water more acid but doesn't work. There is something about my set up that I can't seem to get right.

Thanks for the advice.

[chem geek]

The extra aeration has the pH rise faster from more carbon dioxide outgassing. The higher TA level is also a problem since TA is a measure of the over-carbontion of the water. You should not be raising your TA to 80 ppm. Let it stay at 50 ppm so raise it to 50 if it gets lower.

You can use 50 ppm Borates from boric acid you can get from Duda Diesel or from The Chemistry Store to slow the rate of pH rise. You can use PoolMath to calculate the amount.

[dlleno]

I've taken the advice of chem geek with great success too, btw. big mistake to follow spa store and calculator rules and target TA for a saturation index of 0. In an acrylic spa, pH rise becomes more important than meeting the balance rules -- you can run with slightly "aggressive" water (index below zero) and the lower TA helps control pH rise. I've flirted with TA as low as 30ppm but you have to be very careful to measure often and avoid a precipitous drop in pH.

remember too that adding acid drops both pH and TA. I've also taken the splendid advise here to lower TA on the initial fill: aerate to raise pH, then add acid to lower both.

I've also tried to maintain pH without borates if you are switching to bleach....its tough. get the borates lol