Can't seem to get pH back down

[ccompton]

First, thanks for all the great information y'all provide.

I just moved into a new house with a 'new to me' pool. I took my water in to be tested about two weeks ago. The numbers the pool store came up with were:

Temp 85 (sample was close to an hour old by the time we got there)
FC 8.4
CC 0.1
pH 7.3
TA 84
Adjusted TA 39
CH 333
CYA 151

My test kit arrived the next day and my numbers pretty much aligned with theirs with exception of the pH:
Temp 78
FC 8.2
CC 0.1
pH 7.6
TA 90
Adjusted TA 31
CH 330
CYA 160

I'd used this pool store for several years, and followed their recommendations and had good success with the pool at my old house. They are half way across town from the new house so I'm trying to do more of this myself instead of finding someone closer that I actually trust. They recommended that I add 31lbs baking soda to get the TA up where it should be and 3 cups muriatic acid. That sounded like an incredible amount to be adding and I was unsure of my volume estimate on the pool so I started with 26lbs and 2.5 cups of acid. I retested 48 hours later and TA had come into range, but the pH had gone too high:

Temp 76
FC 7.2
CC 0
pH 8.0+ (demand test took 5 drops to get back to 7.6)
TA 170
Adjusted TA 115
CH 330
CYA 160

From this point I've been watching the pH daily and adding muriatic acid in small batches (about 3-4 cups at a time) to try to get the pH back in line. After adding nearly a gallon over the last week, this morning's numbers are:

Temp 76
FC 4
CC 0
pH 7.8
TA 140
Adjusted TA 90
CH 330
CYA 160

I know my FC is way low and my CYA is way high. The previous owner used only tabs and I've stopped that. I'd like to do a water replacement, but our water table here in North Texas is very high. I'm hoping to wait until mid summer when we have been very dry so there is less chance of damage during a drain and refill. Now that you've read the book, here are my real questions:
1. Given my high CYA and what I've read, my target FC should be in the 10-12 range until I can get my CYA down. Is this correct?
2. Do I just keep adding acid in small batches until I get the pH back in line or should I be doing something different? Just seems like I've added an awful lot in a short time.

Thanks in advance for any advice y'all have. I've heard you like pictures so:

 

[Richard320]

Welcome!

That's a beautiful pool; too bad the pool store had to wreck things.

What test kit did you buy, may I ask? Some of the electronic ones are prone to misreading very quickly.

You are correct about maintaining the high FC to match the high CYA. Poolmath says 12 is the minimum you should never let FC slip below. The problem with that is, your pH readings will always be suspect; the phenol red drops react with FC over 10 and read falsely high.

If you plug all your numbers into Poolmath (use Total Alkalinity, not adjusted, whatever that is) and it should tell you how much acid to add to get to a particular pH. If you then scroll down to the bottom, where it says Effects of Adding Chemicals, plug that dose in and it will tell you how much TA will drop with that addition, roughly. You'll see that it will take a while to lower. The high TA - I would have left the first readings alone - combined with your beautiful waterfall will drive pH up really fast, as you've discovered.

I completely understand not wanting to drain. My first year I was stuck with even higher CYA, and I couldn't drain due to water restrictions. Maintaining a pool with super high CYA can be done, but it's no fun, and I don't recommend it. Anything you can do to lower CYA - use pool water on the lawn, and replace it with the water you would have used on it - will help.

 

[frustratedpoolmom]

Purchase one of the recommended test kits and ditch the pool store's bad advice. Yes, since the pool is clear, you can try and manage with the high CYA as you slowly lower it. Will be tricky, and you need to be able to do your own testing during that time.

Enjoy your pretty pool!

 

[ccompton]

I got the Taylor K-2006.

As for the Adjusted Alkalinity. On the last page of the Taylor book there is a table to do TA adjustments based on pH and high CYA. I'm guessing from your comments that I should be targeting TA based on the test reading and not the adjusted value calculated from that table, correct? If that is so, why the table and the formula?

I'll go with the calculations from PoolMath and see where that takes me.

 

[JasonLion]

Adjusted total alkalinity is only[/ul] used for calculating LSI, which we never use. When we talk about TA, we are always referring to the number straight from the test kit.