My 1st drain and refill of hot tub

[cschnurr]

I have just drained and refilled my tub for the first time.
I am using tap water, my initial value of TA is 250.

After my initial fill I spent many days reducing pH to around 7.0 and aerating.
I found the following thread as a way to reduce TA quicker.

_{https://www.troublefreepool.com/threads/151620-new-fill-questions-on-chemistry-balancing.}
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_{Step 4 of the process states.}
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4. Calculate how much you want to lower your TA, and how much acid you need to add to lower it.​

Could someone please educate me how to calculate how much acid is required to lower TA a specified amount. I couldn't find it on the pool calculator.

Additionally, I live in an area with hard water.
My installer suggested that I could refill using water from my pool.
I don't think he realised it was a salt water pool at about 3400 ppm and CYA~85.
I used tap water for the initial fill for my 1st refill with some sequestrant.
Would this be a problem to have used pool water with this level of salt and CYA??

Thanks

 

[MPurcell]

You don't want to reduce pH below about 7.0, so use PoolMath to lower your pH to that level only, then aerate to increase pH back up, and repeat the sequence.

You can calculate the effects of muriatic acid down at the bottom of PoolMath in the section Effects of adding chemicals. You didn't say what volume your tub is, but for example, to lower pH from 7.8 to 7.0 in a 400 gallon tub would take 1.6 oz of 31.45% muriatic acid. Down at the bottom, you will see that 1.6 oz of 31.45% muriatic acid will lower TA by 16.

I agree that you should not use the pool water. In a chlorine hot tub, you want the CYA to be around 30, no higher than 40. I don't think the salt would interfere with your other chemistry, though. Or you could even get one of those drop in SWCG's, but you really shouldn't have CYA of 90 in a hot tub, even with a SWCG.

 

[pooldv]

More here about setting up a hot tub. How do I use Chlorine in my Spa (or pool)?

 

[cschnurr]

Both your responses describe the method I used.
Thanks for the info.

The thread I referenced seemed to indicate there may be a shortcut which likely drops the pH below 7.0 for a short period of time.

new fill, questions on chemistry balancing

- - - Updated - - -

Both your responses describe the method I used.
Thanks for the info.

The thread I referenced seemed to indicate there may be a shortcut which likely drops the pH below 7.0 for a short period of time.

new fill, questions on chemistry balancing