pH Has Me Stumped???

[Gebo]

t's been 4 months and I just purged my hot tub and getting water rebalanced. It's been overnight and I have run it umpteen times. Used Dichlor to get Cl to 12. ('m gonna use Dichlor until I get CYA to 30 and then switch to liquid Cl). I checked and it was at 11.5 two hours later after initial fill. This morning the Cl was 6.5. Cal was at 150. TA was at 60. All is well....until I check my pH. IT is purple. 8.0 or higher. I then proceeded to add the "Acid Demand". I added one drop and the pH dropped to the really yellow. 7.0 to 7.2. I decided to add 1/2 oz of muriatic acid 34% to my 355 gal of water. Waited an hour and go back and check pH and it is till 8.0 (purple).

You know, I thought after a year I would be an "expert" but I am at a loss. Is the fact I am using Dichlor causing this problem. I use the 871 powder test for the Cl. What am I missing?

 

[Mdragger88]

You’re not missing anything-
Don’t worry with the acid demand test just use PoolMath.
You’re aerating the water so the ph will rise. Add a little more acid to get ph to mid/high 7’s & Stop unnecessary aeration as you’re getting close to a ta of 50.
Dichlor is acidic so every dose will lower ph & ta some too.
Check the ph when the tub is calm.

 

[Gebo]

It was just so purple I didn’t know how high it was. That’s why I was using the acid drop test.

I’m adding muriatic acid in 1/2 oz increments. Thank you!!

 

[JamesW]

It was just so purple I didn’t know how high it was.

Purple is usually chlorine interference.

Can you show a picture?

pH won't go that high from normal processes.

pH rise from aeration and TA is limited to about 8.3, which is not purple.

Genuine high pH requires a strong base like sodium carbonate.

 

[Gebo]

It’s gone down now. I have added total of 2.5 oz acid in .5 oz increments since last night. I quit aeration this morning. I think I’m around 7.6 now.

It just really shook me up that I added 1 drop of acid demand and it dropped pH to 7.0-7.2 from being 8.0+.

 

[Mdragger88]

When ph reads higher than measurable Just put the highest readable measurement from your comparator in poolmath as your “current” and select mid 7’s as your target. Add what it says & repeat this dance until you have a readable ph & can adjust more precisely.
The acid demand thing can get you into trouble trying to extrapolate an un measurable ph for no real reason.
People end up using too much acid in one go then freaking out about that & rushing for soda to correct.

 

[Gebo]

You are correct and awesome! I had finally started doing what you said. Put in pH of 8 and my goal was 7.4. Did it twice and I’m stabilized at 7.4. Thank you!!

 

[Mdragger88]

Now that your ta is down you no longer need to aim for low 7’s -
Aiming for mid to high 7’s is fine & will prevent you dropping your ta too low when you need to add acid.
If ta happens to drop below 40 just use a little baking soda to get it back up to the 50 range. & I mean a little ,
Be light handed- you can always add more later if you need to

 

[Gebo]

This morning I am:

pH 7.4
TA 60
CH 150
Cl 12 (adding Dichlor last night til I get my CYA to 30)

Also added 14 of “pure” boric acid from Duda.

It’s hard to be “light handed” but you speak the truth. If it says add .8 oz, I only add .7 oz.

 

[Mdragger88]

I’ve broken out the food scale a couple of times!
My tub is so small that its easy to overdo it

 

[Gebo]

I definitely use the digital food scale....

 

[Mdragger88]

We’re nerds