how much muriatic acid

We have a 18x48 frame set intex pool. It holds about 5,580 gallons of water. We just filled it with water May 30. We have been adding muriatic acid 1 cup at a time to lower alkalinity. Yesterday we put a cup in at 10 a.m., another cup at 5 p.m. and one at 7:30 p.m. Alkalinity went from 320 to 290 back to 320 and this morning 290. Do I need to put more than I cup at a time? I get my PH up to 7.5 before adding more acid. These are my readings right now.


PH 7.0 ( I am aerating right now)
TC 5.0
CC 0
FC 5.0
Alk 290
Cya 0

Thanks
Peggy

You only need to put in enough to get your pH down to the 7.0 mark. Alk is related to your pH. As you drop pH, the alkalinity will drop. Areating brings the pH back up so you can add more acid. Conceivably, you could areate and keep the pH down in the 7.0 range and your alk will slowly drop off. It just takes a while, that's all.

Michael

There is a rule of thumb for lowering PH but it depends on a reasonable alkalinity. The formula is for .2 PH drop:

Oz muriatic acid = .0008 * pool volume (gallons)

So for a .5 drop, you would need about 12 oz. Your alkalinity will resist the drop so you could probably put in more than that but I would start with 12 anyway. As Mike said, drop it to 7 and keep it there until the alk drops.

I would strongly recommend against using a formula to calculate anything more than a 0.2 pH drop. That's why the formula is limited like that. Your results could be unpredictable.

Michael

Thanks. That's what I have been trying to do. I guess it will just take a while. Is it okay to check ph several times a day and add more acid to keep the ph at 7.0 or should you just do that once a day?

When I have my alkalinity set properly, I am able to hit .4 PH drops right on the money but that does come with experience.

Mark,

I agree, but you have two big BUTs in there:

1. Alk set properly
2. Experience with the pool

That combination can go a long way to hitting a mark. New(ish) folks might not be so lucky! ;)

Michael

I am still a little confused. Should I just check PH and Alk once a day and if needed add acid only once a day?

That's what I plan to do.

I think all you'll waste is time.

Quote:

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Originally Posted by wolfcue

I am still a little confused. Should I just check PH and Alk once a day and if needed add acid only once a day?

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I found the best time to add acid is at the beginning of your circulation cycle and the best time to measure PH is at the end of your circulation cycle. If you are running 24/7, then measure 12 hours after acid addition.

Okay, I will try that. Thanks for the help.