Why did my alk level drop 80 points

[BigK75]

Hey Guys:

Yesterday I added 20 grams of PH down to get the PH down to 7.6 from 7.8.  I did notice the PH went down, but the alk dropped from 120 to about 40.  What should I do?

Claude

[Reese]

The acid lowers both TA and pH.  I'd just leave it, and see if your pH remains stable.  If so, leave things alone.  If not, you can add sodium bicarbonate (baking soda, TA increaser) to raise TA.   Unfortunately that will also raise pH slightly, so you will need to play around to find the proper ratio of acid/bicarb to fine tune your water.

[anne]

Claude, I also find that using dry acid, or pH down to decrease my pH will decrease my TA relatively more than expected. If my pH is pretty high (like 7.8-8), and my TA is right where I want it (like 100-120) I'll actually add baking soda (bicarb) first to increase the TA even higher (maybe 150ish), then add the acid. Bicarb itself has a pH of about 8.3, so it cannot increase your water's pH more than that, so most of the effect will be on the TA. Then when you add the acid, both the TA and pH will drop into the range you want.

I'm sure this is not the most common way to deal with this problem, but it has worked very well for me. My water has historically wanted to creep up in pH and down in TA, and this is how I'd handle it. Mysteriously, for the last few months, (since the last fill) I have had amazingly steady pH.

[neocacher]

Get your pH where you want it, and dont worry about alkalinity.  If you have high pH, you have to accept whatever alkalinity you get when you lower your pH, otherwise you will chase it for 2 weeks, like i did.

It is a TOUGH fight if you have high pH and low ALK, so dont fight the fight.  Alkalinity is only a measure of so-called stability, and is meaningless otherwise.  Whether you alk is high or low will not ruin your tub, where a high pH or Low pH can destroy it.

Neo

[Pathfinder]

20 grams is a lot to lower 2 points     7.8 is still acceptable with the use of the hot tub your ph would have went down in the good range.    If you are on a floater program
and are not using the tub that often only leave a puck in the floater  for the fact the cl/br not being used the Ph will climb.  Its better to have your ph on the higher side then the lower side

[Chad]

Its better to have your ph on the higher side then the lower side

I always thought that the lower the pH the better, as long as it's above 7.2 b/c the lower it is the higher the % of the chlorine becomes hypochlorous acid(the "killing" form.)
http://www.rhtubs.com/chlorine.htm#Introduction

[Reese]

I always thought that the lower the pH the better

Depends on what is being used for sanitizer, among other things.  For example, bromine has a low pH, and its effectiveness is not as sensitive to higher pH, so it makes sense to start at a higher pH since it will tend to drift down as the bromine is released -- while as you stated, chlorine needs a lower pH.  Some alternative sanitizer/enzyme programs require a higher pH to work effectively.  TA, hardness, and temp also come into play when determining the proper pH for a tub.

[wmccall]

Hey Guys:

Yesterday I added 20 grams of PH down to get the PH down to 7.6 from 7.8.  I did notice the PH went down, but the alk dropped from 120 to about 40.  What should I do?

Claude

This is where I like to specify that PH has an acceptable range, not a target number.  7.8 by most references is right at the top end of acceptable and with a alk of 120, I could see that coming.  I think you started off with acceptable numbers and were chasing ellusive ideal ones.