optimal order of adding muriatic acid and liquid chlorine

[ramblinwreck001]

Is there an optimal order to add these: acid before liquid chlorine, or liquid chlorine before acid?

I am not talking about huge changes like startup or SLAM. I'm talking about normal small maintenance doses during the week. I usually add in the evenings. I wait a little bit between adding the two chemicals.

Most 'order of adding' chemicals articles I see suggest adjusting the pH first before adding sanitizer, but these seem to be talking about large adjustments which is not what I'm asking about here. What got me thinking is liquid chlorine additions raise the pH a little. I understand this is a net-zero effect, as LC temporarily raises the pH but then it drops again as the chlorine consumed. However, I add LC at night where there is little-to-no chlorine consumption, which suggests my pH remains slightly elevated all night due to this effect.

Would adding acid after the liquid chlorine help minimize this effect? Or is the end result the same regardless of the order? I don't know the chemistry well enough to know if it matters, but it seems (?) that a given amount of muriatic acid has larger downward effect when the starting pH is higher, which could suggest adding LC before acid is better.

And yes, I fully realize I'm overthinking it and the difference, if any, is small.
But this is a zero-cost thing for me so if one way is better then I'd like to adopt that approach.
What do y'all do?

 

[Newdude]

And yes, I fully realize I'm overthinking it and the difference (if any) is small.

You said it.

I test them both and adjust accordingly. If one is ever so slightly skewed from the other after, I feel i'm still doing better than the 99.99%

Let's see what @JoyfulNoise and @mgtfp have to say about it.

 

[JoyfulNoise]

Makes no difference which order you add them in. If you want to add chlorine at night and then adjust pH in the morning, that's fine. If you want to add them 15 minutes apart, so be it. Doesn't matter either way.

 

[ramblinwreck001]

If you want to add chlorine at night and then adjust pH in the morning, that's fine. If you want to add them 15 minutes apart, so be it. Doesn't matter either way.

Surely there has to be some difference in overnight pH level between these two methods?

A little more context. Previously, I was actually doing LC at night and adjust pH next morning like you say, but always found higher than expected pH in the morning. It occurred to me that maybe my evening LC additions were exacerbating this, since the chlorine had been added but not yet consumed by the time I check pH in the morning (assuming little/no overnight chlorine consumption). Yes, the pH elevation is temporary, but in this case temporary seems to be all night. This is what got me thinking about this.

In the summer when water temps are higher, I'm always near the higher end of the safe CSI level (no issue right now with low water temp), which is why I moved my acid additions to the evening.

 

[JoyfulNoise]

pH is far less important than most make it out to be. You can safely swim and sanitize a pool at any pH value between 7.2 and 8.0. If you keep your TA on the low end then managing CSI at any pH value is not really an issue. As far as damage that might occur … that typically happens when pH is allowed to be out of range for weeks or months on end. So, if you’re doing daily management of your pool water, then there is no discernible difference in when you treat pH or chlorine. It’s splitting hairs at this point …

 

[ramblinwreck001]

I'm a pro at splitting hairs.

Thanks, your reply helps put things in context. I do mostly keep my TA between 60-70, but still I find that my pool's pH will climb above 8.0 quickly (few days) if I don't stay on top of it with acid additions. I recently had automation installed and now I scheduled my spillovers, which seems to have helped a little. I got my pool last summer and didn't monitor CSI then, but am doing so now and want to be better prepared/educated for this upcoming season.

 

[mgtfp]

I don't know the chemistry well enough to know if it matters, but it seems (?) that a given amount of muriatic acid has larger downward effect when the starting pH is higher, which could suggest adding LC before acid is better.

But while pH is elevated after the LC addition, TA will also be slightly higher because you shift a little bit to the right in the Carbonate and CYA equilibriums, so that the following MA addition is slightly more buffered. In the end it's six one, and half a dozen the other.

I would make it a general rule to add acid first, which certainly is more relevant when Slamming.

It's like indicating when changing lanes: Make it a habit even if feels stupid to do so every single time when you are alone on the freeway in the middle of the night. But by making it a habit you will actually be indicating when you have missed that car in the blind spot and give the other driver the chance to compensate for your mistake.

When you add acid first, you are kind of forced to test pH while FC is definitely below 10, and don't forget to do so when doing your once in a lifetime Slam.

During a Slam you will like that also reduce the max pH, giving you a lower chance to end up with metal stains should so far unnoticed metals be in you pool water.