Metals PH and Chlorine

[Laurie Critchfield]

I have Iron in my water and had staining. Did the Ascorbic acid treatment added Polyquat, sequestrant, some of the stains lifted. I must have other stains that are not organic or metal but one problem at a time. My question relates to the natural tendency of my PH to rise. It takes a lot of muratic acid to keep my PH at 7.2, it will settle at about 8.2 if left alone. If I understand the instructions, if PH and Chlorine are high metals precipitate back out. So... if I need to shock I should bring the PH to 7.2 and keep it there as long as the chlorine is high, but other than that is it ok to leave the PH high as long as the chlorine is at normal level for my CYA? Then a follow up question would be to over winter, do I need to keep adding sequestrant all winter? A PH of 7.8 is not too hard to maintain during the swimming season and the CSI is much better at negative .01.

Current (finished muratic acid treatment and PH is rising on its own)
chlorine 0
PH 7.5
TA 80
CH 230
CYA 40
CSI .3

 

[Swampwoman]

Laurie, I'm a bit confused re the source of your information.

Here's my understanding...which of course, depends on the concentration of iron

High ph will precipitate metals, period.
High chlorine, via elevated ph, will oxidize and precipitate metals, period.
High chlorine will also erode your sequestrant quicker.
Note: By high, I mean slam/shock value.

So, in managing metals, it is IME generally best to:

A) Avoid slamming/shocking and to avoid the need to do so, maintain the [fc/cya][/FC/cya] - which is the founding principal of TFP

B) Control ph to 7.2-7.4. With a few exceptions. eg. If you're using Metal Magic, you can run 7.6 ish per instruction as it will reduce the ph a bit. Sometimes to control ph, you'll find its easier to do with lower TA level also easier to do when pool is covered with solar cover overnight, etc.

For winter, I've found a full dose of sequestrant best, but that's likely because I've typically elevated my FC as high as possible, but below slam value, a few days prior to closing. Because your pool is covered in winter, once closed, ph will not rise. For this reason, right before closing, I would also avoid dropping ph tooo low (eg I'd let mine red at 7.4.)

Hope that helps a bit.

Other metal mgmt strategies include using softened water to top up, ergo greatly reducing the iron load, and prefiltering to get some, but not all, of iron in its oxidized state.

 

[Laurie Critchfield]

Maybe I need to read more. What do you mean by high chlorine via elevated ph? I normally do not have to slam/shock as I maintain appropriate chlorine levels and have had no problems. I was thinking more about when I open the pool in spring I usually elevate the chlorine but I can probably get by without doing that.

When you say the PH will not rise because it is covered, I do not find that to be the case. The pool has been covered for about 3 weeks now to keep the leaves out. I have left the filter running to circulate the ascorbic acid and polyquat. The PH stayed low (7.2) for about 2 weeks after the acid treatment but is climbing now all on its own. I know where it will go without intervention as it is usually about 8.2 when I open it in the spring. I have to add about a gallon of muratic acid a week to maintain a PH near 7.2. What is IME?

 

[Swampwoman]

What do you mean by high chlorine via elevated ph?

Sorry, I could have worded that better. I mean slam-level chlorine oxidizes the metal so that it precipitates and that simultaneously ph temporarily spikes, aiding in the unintended precipitation of metals/staining.

IME=in my experience

The jist of my comment is that no, keeping ph low when slamming will not necessarily prevent metal precipitation, so its best to avoid slamming, and no, letting ph get high, eg 7.8, while the chlorine is low will not prevent precipitation/staining either.

High ph and slam-level FC should both be avoided to manage metals most effectively.

Regarding your ph rising when covered, my TA is usually a bit lower than yours and barely rises at all when I'm using the solar cover heavily. But I also have borates at 50 ppm in the water, so maybe that helps keep it more stable.

It is always hardest to keep ph like, eg 7.2, because most pools "want" to run higher Thats one of the reasons I've favored Metal Magic...it seems in my case to "keep" the metals sequestered at higher ph levels. With it I run at 7.6 ph. BUT I've also done a lot to lower my iron concentration, such as refilling from softened water plumbed to the pool spigot, prefiltering, etc.

Hope that clarifies my comments a bit.