Control, I must learn control!

[UsefulTech]

Things seem OK for now, but I’m having trouble with my adjustments. My Chlorine and pH results have been double what my target was using the Pool Calculator. My pool is 18x36. 4.5 in the shallow end and 8.5 in the deep end. Average of 6.5 says 31,500; using CAD I got 38,000 gallons. So I used 35,000.

This is a newly filled pool using city water. They generally have lots of chlorine and the tap checked 3.5. I started the pump (ejecting clouds of debris) and ran it for about 3 hours before running the 1st full test. It confirmed a basic test that the chlorine was nearly gone. The water has remained clear, but felt I should shock it. I added 415 oz of 10% Cl and 40oz of 31% Muriatic Acid for the pH. 3hours later (11PM) the FC was17.5 and pH climbed slightly. With no CYA, I had hoped to shock at 8, not 17.5.

This morning the FC was still 17, but the pH had risen to 8.2. I Added 70oz muriatic acid, and 3 lbs of CYA to “begin” stabilizing. Pool Calc suggested 12lbs. I hoped for 7.5pH, not 7.2.

I’m just wondering if these ‘missed’ targets are typical when starting up (I suspect I made a mistake in my calculations)?
Is there an order I should follow or are there higher priorities I should be concerned about?
Any suggestions on how to estimate my flow rate?
I’d appreciate any suggestions or next steps.

8PM- water clear, 67 deg
FC 0.5
CC 0.0
pH 7.8
TA 120
CH 120
CYA 0.0
Added 415 oz of 10% Cl and 40oz of 31% Muriatic Acid

11PM- water clear
FC 17
CC <.5
pH 8
No action

6AM- water clear, 67 deg
FC 17
CC .25
pH 8.2
TA 120
CH 100?
CYA 0.0
Added 70oz muriatic acid, and 3 lbs of CYA

11AM- water clear, 69 deg (woohoo, swimming in no time)
Basic TC off the scale >5
pH 7.2
No action

 

[Bama Rambler]

I get 26,000 gallons for a pool that size. Try that in the pool calc a few times and see if the additions aren't closer.

 

[UsefulTech]

Dave,
I forgot to specify mine is a rectangular pool. But I've re-verified my values for 31,500. If the difference wasn't such a large amount I wouldn't worry about it. Can you provide your calculations or resource? I'd like to find my error. (control thing I have)

Regardless, I plan to use the 26,000 for my future calculations.

And thanks to the entire group for a great forum!
Dan

 

[BadOleRoss]

My pool is the same size but with grecian ends.....I use 27,400.

 

[Bama Rambler]

I use modeling software and made some assumptions about slopes.

 

[UsefulTech]

My pH is lower than 6.8 now! Is it still safe to swim?

I'm aerating with my coping jets hoping to increase the pH. Is it urgent enough that I should add soda ash / washing soda? Where would I find that?

Should I take any action.

How I got here:
Since the original post, I've completed adding 8lbs of CYA. It's not fully dissolved, but it was near 20 this morning. The shock level dropped from 17 to 7 yesterday, and held overnight. I didn't know that pH levels should be ignored when FC is over 10 when I added the muratic acid. I had seen a post that said pH should never exceed 8.0, so I attacked it aggressively. Now, the chlorine level has dropped, and the pH is following.

6AM- water clear, 73 deg
FC 7
CC .25
pH 6.8
TA 120
CH 100?
CYA 20.0
Added ~8 lbs of CYA

 

[Bama Rambler]

If you're sure it's no lower than 6.8 and you're aerating, it's fine. Now go get to manually raising that pH (just don't tell anybody it's actually swimming)