Pool Math...I am not sure I am understanding correctly.

[pypeke]

Using pool math, I enter the gallons of water in my pool. Then, I enter my current pH of 8.2 and what number I want to bring it down to...7.5. It says 22 oz of 31.45% Muratic Acid.

8.2 - 7.5 = 0.7 (amount it should lower)

If I use the section at the bottom "Effects of Adding Chemicals", and enter 22 oz of 31.45% Muratic Acid, it says it will lower pH by 0.33.

I think the note (see below in blue) means that because my pH is above 7.8 , then my 8.2 is NOT a small change. Therefore, that is why there is a discrepancy between the amount of MA suggested in the two different calculations.

So should I go by the first calculation of adding 22 oz because adding less is better? Then add more again after retesting? This is best?

Or should I go by "Effects of Adding Chemicals", and add 46 oz of MA to lower the pH by 0.69 (close to 0.7). Run a risk of lowering pH too much?

thanks.


"[FONT=&quot]Note: pH calculations are not exact. These numbers are only suggestive of the relative magnitude of the pH change you can expect. Small changes, +-0.4, with pH between 7.2-7.8, TA around 80-120, and Borate near zero will be approximately correct. The further you go from those ranges the less these pH changes will correspond to reality."



[/FONT]

 

[mickey4paws]

I would go with the pool math numbers

 

[jblizzle]

Make sure that for any pH adjustment your TA is also set in the NOW column.

The "Effects ..." calculation makes assumptions about the TA and other parameters in your pool so it may not be as accurate for pH adjustments.

 

[pypeke]

mickey4paws, thanks. They are both from pool math.

jblizzle, thanks. I wondered if some of the other numbers played into the calculations.

So set the gallons of water, the pH, TA and other boxes even if I am changing only one parameter? (I have only been entering the boxes on the one I needed to change.)

For example, if my FC is a good number already, I would fill in the goal and target as the same number because I am not changing the FC?

thanks again!

 

[jblizzle]

It is always a good idea to have every box filled in as some things are related.

The FC is independent, but many of the others feed into the pH adjustment.
And just about all are needed for the CSI calculation.

 

[JoyfulNoise]

You want to be very careful with pH adjustments. The difference in amounts is because the Effects section uses some static assumptions about TA, starting pH etc.

When adjusting pH, I would only use 0.2-0.3 increments at most and also use the effects section to see what the volume added does to TA. You don’t want to lower TA more than 10ppm at a time.

 

[pypeke]

Thank you. My pH is my only problem this year. I bring it down and a few days later it is back up past 8.2. It is darker than the 8.2 sample so I don't know what the number actually is.

 

[splashpad]

Can you share a full set of test results?

One of the members might be able to see something

 

[pypeke]

thanks.

FC 4.5
CC 0
pH 8.2 +++
CYA 40
TA 80
CH 100

After adding chlorine and muratic acid

FC 7
CC 0
pH 7.3
CYA 40
TA 70
CH 100

If the pH goes back up, I will lower the TA to 60.

 

[JoyfulNoise]

What is the pH/TA/CH of your fill water?

 

[pypeke]

Well, another senior moment for me...I will have to check it.