hating water care right now....

[anne]

I'm hoping that someon can find a big error in my approach to water chemistry, because I can not make any sense of the pH, TA problems that I have been having. The following progression has been over the last week, since I returned from a 2 week vacation. I use a Taylor test kit, I think I perform all the tests very accurately (minding drop technique, following all instructions, etc). I use chlorine, MPS to shock, have ozone, and about a 400 gal tub.

Sunday:
FOUND: cloudy water (I've been gone- housesitter was caring for things but unlikely any sanitizer in a few days) I did not measure TA, pH (yeah, guess I should have)  
ADDED: 3.5 TBSP chlorine (a little over 9X normal dose), and a bit later 2 oz MPS

Monday: (water clearer)
FOUND: FC=1, TC=5. pH 8, and I cannot remember TA. Thought TC level was odd, but considered that I might have added the chlorine and MPS to close together the day before.
ADDED: 2 more oz MPS.
Few hrs later:
FOUND: FC=5, TC=0 checked pH again to see if MPS affected: still 8.0, TA 125.
ADDED: 1.5 oz dry acid

Tuesday: (water crystal clear)
FOUND: pH 7.7, TA 80
ADDED: 6 TBSP to get TA back up before I add more acid

Wednesday:
FOUND: pH 8, TA 130
ADDED: 2 oz dry acid

Thursday: no time to measure anything

Friday:
FOUND pH still 8.0, TA 60!
........


I'm at a loss. Every time I add dry acid, I have a huge decrease in my TA, and little affect on pH. I know I should be taking chlorine level into consideration, but if anything, wouldn't  a high chl level make my pH look falsely LOW??? With all the chlorine, mps and acid I have added, what gives??  

[Stemay]

It all sounds complicated for me!  How about doing a water dump and starting from scratch?  Sounds like things went haywire while you were on vacation.

[The_real_Clown_Shoes]

Anne, if you can get your pH in range, your alkalinity will be perfectly fine perching at 80 ppm.  Don't worry about getting it exactly in between 125 - 150, that's just a rule of thumb to prevent your alkalinity from dipping too low.

I didn't read too in-depth on what your pH was after you added the TA increaser, but when you add alkalinity your pH typically doesn't rise too much.

What's your source water like?  Would adding fresh water bring up or bring down the TA and pH?

[Vinny]

anne,

First thng is don't take combined chlorine readings for a few days after shocking with MPS. It skews the numbers.

Second, I believe that TA will go down before PH. I've also read that if you mix the water (jets on) PH changes before TA and if you leave the water still TA changes before PH ... but I don't know if this is true.

I've also said this before - worry about PH, not so much on alkalinity. From what I've read, alkalinity only helps keep the PH stable - it seems to be doing the job here!

[anne]

Stemay-
I considered doing just that, but I only changed the water about a month ago, and I ALWAYS seem to be fighting high pH, this is just a bit more extreme that normal.

Vinny-
that is a good thing to know about MPS skewing TC readings, cuz today (after posting) I checked my FC and TC and was about to pull my hair out seeing that my TC was still supposedly 1. I'll leave that alone. Water certainly smells nice.

Giraffe- my water source has a kind a high pH, so I dont know that partial drainage and refill would help that much.

I got irritated and added 3 oz acid this morning, (pH was 8, TA was 60, so I knew I'd bottom out my TA, but every time I adjust TA first, my pH skyrockets.)

Now I'm at a pH of about 7.1 and TA of like 20. I've never seen it so low. Off to add baking soda.......

As a related but slightly separate question, does anyone out there rely on the Taylor kit "acid demand" and "base demand" tests to decide how much to add?

[hottub.pool_boy]

Don't try balancing(Alk.,ph,ch) your spa with a high chlorine reading. Wait for the chlorine to fall, then balance.

For the future, if the tubs out of whack, balance FIRST, then shock.

[anne]

For the future, if the tubs out of whack, balance FIRST, then shock.

I'll keep that in mind. oops. I was impatient to get my water clear ASAP after not having a hot tub for over 2 weeks!