Low Alk OK?

Jump to latest Follow Reply
W

wolverinefan99

0
Sep 14, 2018
7
Detroit, MI
Hi All

New hot tub here. Purged with Ahhsome and refilled with well water. I read the stickies at the top of the forum and am using sodium bisulfate to lower pH/Alk and aeration to raise pH. I've been able to stabilize the pH at 7.8 with Alk at 20. Any higher alkalinity (even at 40-50) and the pH is way over 8.0. Br = 3.5, CH = 175. Any thoughts here? Do I just leave the Alk at 20 (or maybe lower a bit more to get the Ph at 7.4 - 7.6)? Seems like there is no way to get the Alk into the recommended range of 80 - 120 without sending the pH over 8.0

Thanks
 
There should be a sticky about the TA/PH in a hot tub.

You ever see a dog chase his tail. That's how it was when I was trying to get my TA to 80 and PH within range. It's fine for TA to be between 40-50. After that, PH should remain steady when you get it between 7.2-7.6
 
To reaffirm what most people are saying here, I was chasing my tail trying to get TA up to 80 while maintaining a proper pH. When I finally gave up and let it drop to 40-50, my pH remained at a steady 7.4/7.5. My question is why do most test kits (including Taylor) recommend a minimum TA of 80 when 40-50 seems to work so much better?
 
jmasone said:
To reaffirm what most people are saying here, I was chasing my tail trying to get TA up to 80 while maintaining a proper pH. When I finally gave up and let it drop to 40-50, my pH remained at a steady 7.4/7.5. My question is why do most test kits (including Taylor) recommend a minimum TA of 80 when 40-50 seems to work so much better?
Click to expand...
Two things come to mind right away. First, there's "industry specs" that are repeated and never changed. Secondly, they expect you to use dichlor or trichlor, both of which are acidic and will pull down your pH. If you balance your water to the point your pH no longer rises with aeration, that's great for bleach, but you'll drop your pH with dichlor/trichlor.

I've done it myself. New fill, balanced the water in a couple hours with a pH around 7.4-7.5, then didn't check pH for a week or two because I was used to it being rock solid. It was below 7 when I finally checked it, because I forgot that dichlor was acidic. So recommending a higher TA probably ensures people don't tank their pH by running the TA down to zero using acidic chlorine sources. My guess is because while a higher pH may not be the best to sit in, a low pH with corrode your hot tub heater and they don't want lots of complaints on that.
 
wolverinefan99 said:
Yes. After a couple of days, TA dropped to more like 15 (saw some color change with drop 1, full change with drop 2) and now pH is at 7.4. Seems like keeping the TA at 15-20 is the only way I am going to keep pH at 7.4 - 7.8 with aeration.
Click to expand...
Maybe someone with more knowledge can chime in here but those levels seem a bit low to me. I would slowly bump up the PH about .1 PPM at a time with Borax until you get the PH stable at about 7.5 to 7.6. I wonder what AK you would end up with?
 
Try keeping the pH at 7.8.

A certain percentage of the TA turns into carbon dioxide.

The carbon dioxide is what gets lost when the water is hot or agitated (aerated). It's the same process as a beer or a soda going flat by losing carbon dioxide when warm or shaken.

Once the carbon dioxide is lost, more is created by the bicarbonate (TA) being converted into carbon dioxide. When bicarbonate turns into carbon dioxide the pH goes up.

A lower TA reduces the amount of carbon dioxide in the water. So, you have less pH rise.

Also, the percentage of bicarbonate that turns into carbon dioxide is determined by the pH.

pH..........%CO2
6.35.........50.0
7.2...........12.4
7.4.............8.2
7.6.............5.3
7.8.............3.4
7.9.............2.7
8.0.............2.2
8.35...........1.0

So, you can see that there is about 2.4 x more carbon dioxide at a pH of 7.4 compared to the amount of carbon dioxide at a pH of 7.8 at the same TA.

There is about 7.3 times as much carbon dioxide at a pH of 7.2 and a TA of 80 as there is at a pH of 7.8 and a TA of 40.

The best way to reduce pH rise is to keep the amount of carbon dioxide to a minimum. That means a lower TA and a higher pH.

Typically, for a hot tub, a TA of 40 to 60 with a pH of about 7.8 results in a stable pH.

If you can get the amount of carbon dioxide low enough, it will reach equilibrium with the carbon dioxide in the air and the pH will not rise any more.
 

Enjoying this content?

Support TFP with a donation.

Give Support
That's so cool to have that level of technical explanation here. Thank you. I would only like to add that If one is using the saturation index to target balanced water, note that for an acrylic spa you can run with a negative index without fear of certain destruction because there are no materials like gunite that get cranky in aggressive water

With that, I dont target TA I target pH and let TA fall to where it needs to be. I've gone as low as 30ppm but caution that going lower than that you risk a precipitous drop in pH
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply