Calculating amount of pH for reducing TA

[mrmodo]

Hi Everyone

I've been reading the great guides on water care.

I've been reading the one on reducing TA. I'm in a hard water area so always have a high TA reading.

Quote

2. Calculate how much you want to lower your TA, and how much acid you need to add to lower it.

So with regards to step 2 on the TA guide. I'm using the sites 

http://poolcalculator.com/ and https://www.troublefreepool.com/calc.html

The TA part will work out how much I require to increase TA. 

But to reduce it am I doing this right by

1. Entering current TA value and Goal

e.g 300ppm with a goal of 60ppm

2. Entering pH value and goal

e.g 8.0 and 7.5

It then tells me I need 1.8oz of dry acid to reduce the TA down to 60ppm which I then can following the remaining steps of adding half and aerating for 30 mins, etc

(Note - This is for a 350 gallon tub)

Does this sound right?

Thanks

 

[MPurcell]

No. Use the pH section to calculate how much dry acid you need to reduce the pH to 7.0 from where it is now. Then use the "Effects of Adding Chemicals" section at the bottom of the calculator to calculate how much that amount of dry acid will reduce TA. However, do not lower pH below 7.0 because it is not good for equipment or for people.

The process is to lower the pH to 7.0 and then aerate to bring the pH back up to a high level, and then repeat the process until you get your TA down to where you want it.

I'm not clear about your numbers, but if your TA is 300 and you want it to be 60, and your pH is high, say 8.0, then in 350 gallons:

reduce pH from 8.0 to 7.0 requires 5.4 ounces by weight or 3.6 ounces by volume of dry acid

The calculator at the bottom will probably give you a different number for the amount of pH reduction since the caluclation depends on many factors and is not very accurate at those numbers.

The only way to do it really is to add chemicals and then use your test kit to get actual readings, and that will guide you. You must have a proper test kit such as the Taylor K-2006 for chlorine or K-2106 for bromine in order to get accurate readings.

If the numbers mentioned are accurate, you will probably have to go through the pH reduction by acid and increase by aeration process a number of times to get TA where you want it. In my chlorine tub with calcium hardness of 125 ppm I run TA at about 80 ppm and my pH is stable around 7.4 or 7.5 when I don't do a lot of aeration.

 

[mrmodo]

Hi MPurcell

Thanks for the reply

Yes, I think I understand the aeration method now. Initially, I was using the calculator to work out how much dry acid is required to reduce the desired level of 7.5, rather than 7.0.

I have never used the aeration method before. I live in a hard water area and up to now, I would balance the water on refilling whilst still cold. 

The TA level would generally always be high 180+. I would normally dose with a large amount of dry acid (approx a cupful). This would generally knock the TA down to around 80-120 which would be in the OK range on the test strips

Of course, this would also send the water acidic. However, I would find that during the heat up the pH would naturally rise to a reasonable level. It could then be tweaked with pH adjusters to get to the right level.

[arobbert]

I would add that you want to do this process slowly because sometimes you can over shoot. I experienced this lately. Once you get your levels in the ballpark give it a 12 hour rest and proceed at a slower pace Always aerate (a pain in the winter). If you lower the PH to much and then don't aerate you can end up with lower than desired PH levels. 

[mrmodo]

Hi 

Yes, we're in hard water area and I find the trick is using the right amount of dry acid - too little and it make's not different, too much and you overshoot.

Read other posts on here It's not clearer TA does this, with the need for higher quantities of dry acid required for high levels of TA