How to apply ph minus

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How to apply ph minus

Postby Marcus » Sat 08 Dec, 2007 11:04

I have a 71.4 cubic meter pool and my ph reading is 8.4

I thought it was simple for the the second test on the test kit revealed that I should apply about 1750ml of Hydrochloric acid.

According to the bottle of hydrochloric acid I should add 4,200 cc which I think is 4.2ml ( doesn't seem right)

I was given a sheet from the pool shop that calculated what I needed to apply for my pool. It says if the ph is 8.4 the acid dose should then be of 5.1408. At the top of the column it says (ltr) but I suppose the numbers are cc beacause it just seems like a more accurate reading of the calculation shown on the Hydrochloric acid bottle.

I would be really relieved if you could tell me how many ml. of ph minus i should add to my pool.

Thank you


Re: How to apply ph minus

Postby Marcus » Sat 08 Dec, 2007 11:35

I was getting confused for on the bottle it uses "," between numbers and on the swimming pool shop it uses "."
It seems the shop put used the wrong separator.
So what I suppose is that I have to add a 5 liters of hydrochloric acid but should do little by little in order to avoid the corrosion of pipes. Which would mean adding 1.5ltr set the pump to recirculate for about 3 hours test ph and then add more.
I should do this in the evening to avoid sun?

I was getting confused for I thought adding 5 liters was a lot as I thought the chemicals would last longer.
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Postby mr_clean » Sat 08 Dec, 2007 23:39

your correct in not adding alot of acid at once so nothing happens to your pool.

Do you have a full set of your chemical readings?
getting PH & TA in range will help slow down chemical usage with acid.
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Postby chem geek » Sun 09 Dec, 2007 03:28

The actual amount of Muriatic Acid (31.45% Hydrochloric Acid) that you need to add depends on the Total Alkalinity (TA) and Cyanuric Acid (CYA) level since these are pH buffers. With a TA of 100 ppm and a CYA of 40 ppm, the amount for a 71,400 liter pool would be 1400 ml (cc) or 1.4 liters. By the way, milliliters (ml) is the same as cubic centimeters (cm) and there are 1000 of these in one liter and there are 1000 liters in one cubic meter.

As mr_clean said, you want to add less acid than you calculate since you can always add more and you don't want to go too far. Once you are more familiar with the process, you can trust your calculations better, but other than my spreadsheet, there isn't a calculator that accounts for the initial pH/TA/CYA. If you use the drop-based acid/base demand tests, then those can give you approximate values that are "real" and will work regardless of pH/TA/CYA, but they generally don't have enough granularity to be accurate.

Also, if the TA is high, then the pH will have a tendency to rise so lowering the TA will help. As mr_clean says, if you post a full set of numbers we can give you more assistance. Free Chlorine (FC), Combined Chlorine (CC), pH, Total Alkalinity (TA), Cyanuric Acid (CYA), Calcium Hardness (CH) are what is normally needed to be known and are what can be accurately measured from a Taylor K-2006 test kit.


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