Another pH TA question

[AltaNate]

First season managing pool which as yet is only just being used as water temperature starts at 22°C rising to 24°C by late afternoon.
Switched from previous owner using pucks to liquid chlorine and muratic acid thanks to recommendations on TFP.

Latest test results
FC 10
CC 10
pH 8.2
TA 120
CYA 80
CH 360

The pH is bouncing back up over 4-5 days. So looking to reduce TA steadily (it has already come down). Not filling that much so only a slight affect.
Read: “Aerate until pH rises to around 7.6 (the only way to raise PH without also raising TA)” and “Lowering the PH back to 7.0-7.2 more frequently will also speed up the process”

Question1: when adding muratic acid, if I don’t aerate will the TA increase with pH or stay lower?
Question2: can I reduce pH by a large value in one hit, or do I need to do it step by step?

 

[mgtfp]

What lowers TA is the acid, the TA decrease is directly proportional to the amount of added acid. Then you want to have pH rise back up without taking TA back up.

This is done by letting carbon dioxide outgas, which raises pH, put not TA (this is in fact the only way to raise pH without raising TA - as soon as you start adding chemicals to raise pH, TA gets raised too).

Aeration just encourages more CO2 outgassing, it doesn't change the principal, it just speeds up the pH rise so you can add more acid sooner. It's not "needed", you can also just wait until pH has risen back again on its own (by CO2 outgassing that happens all the time via the water surface), without extra forced aeration, and then just add more acid when you'd do it anyway. The result will be the same, it will just take a bit longer.

Don't lower pH below 7, do it in stages.

 

[AltaNate]

Ok thanks…
I’ll aerate a little by positioning the returns to allow flow to break the surface - best I can do presently. I want to get the TA lower to reduce amount of acid adding/purchasing.

So no problem adding the correct volume of acid in one application to go from 8.2 to 7.2 (1250ml for my acid strength and pool size)?

 

[mgtfp]

I wouldn't add that much acid in one go. The PoolMath calculations get less accurate for large changes, and small inaccuracies for example in TA have a larger impact on the result. Your pH is likely above 8.2, so that would save you probably, but I wouldn't count on it.

We generally say, don't reduce pH by more then about 0.4 in one step.

Add half that acid amount, let the pump mix the water for 30 minutes, then retest and recalculate the next acid addition.

 

[AltaNate]

Thanks for advice. I thought I’d read somewhere about not dropping by a larger value. Agreed it is probably above 8.2. Doing that today.

 

[mgtfp]

By the way: I'd recommend to add the FAS/DPD reagents to your K1005:

R-0871-C ¡Al mejor precio! - Analizar Agua

Reactivo FAS-DPD, 60 mL

analizaragua.es

and

R-0870-I ¡Al mejor precio! - Analizar Agua

Reactivo DPD POLVO, 10 g

analizaragua.es

The R-0003 for the CC test should be in your kit.


Test instructions:

FAS-DPD Chlorine Test

The FAS-DPD chlorine test is used to find the level of Free Chlorine in the … Read more…

www.troublefreepool.com

 

[AltaNate]

By the way: I'd recommend to add the FAS/DPD reagents to your K1005:

Would this replace or supplement the Chlorine DPD in my K1005? On paper they appear to test similar things except accuracy and increased range.

 

[mgtfp]

The FAS/DPD is more accurate, allows testing higher levels, and takes the subjectivity out of the test. Instead of comparing colour shades, you add and count drops until you get a transition from pink to colourless.

It is considered a prerequisite to apply the TFP method and maintain the recommended FC/CYA Levels.

Doing a SLAM without FAS/DPD is actually more dump and pray instead of maintaining a defined "shock" level for an extended period.