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New fill questions

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Hello, I've been away for awhile but recently got a new "portable" spa.  Holds about 200 gallons of water.  I had a question about start up/new fill I couldn't find the answer to.  My tap water is a bit acidic but when I start with a new fill the pH goes up to over 8.4 while heating up, I'm assuming do to aeration.  It takes about 18 hours to heat the tub (110V) and the jets are on low the whole time raising the pH.  I've figured out how much dry acid to use to get the tub in the 7.6 range.  I'm wondering if I can add the dry acid when the tub is cold and the water is still acidic so that it will be balance when the tub is hot after the start up process.  I'm using the Dichlor/Bleach method for sanitation.  What I would like to do is add calcium, baking soda,  dry acid and dichlor as soon as the tub is filled so I can use it the next night when its heated up and have the water balanced.  Currently I am adding calcium, baking soda and dichlor as soon as the tub is filled cold and then adjust the pH after it is warmed up and the pH has gone up due to aeration. But now I know how much dry acid I need to get it to where it needs to be when the tub water is hot and hoping to add it in when it is cold before it is heated up.  Any thoughts?

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I also have acidic water (6.6) with low TA (40is) and generally wait until the water warms up a bit before balancing.  Your test kit may also have limits on accuracy at low temps. You dont need it all the way but 70 or higher would be preferred.

You didn't mention what your TA is or how you are testing the water. 


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I'm using testing strips which is a challenge.  I also have low alkalinity soft water.  I have the amounts of alkalinity and calcium to add figured out but the acid after aeration has been a challenge and takes a lot of time waiting between additions of dry acid to get it right.  I was thinking the same thing, maybe wait for the tub to get warmer before adding the acid.  Thanks for the help.

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