Which is more important: Ph at 7.2 to prevent metal stains or at 7.6+ for SWG?

[PoolESQ]

Title pretty much sums it up. Unfortunately, my pool was filled by and is replenished with well water with a moderate level of iron. After a few weeks, I started noticing metal stains appearing around the pool. Did the vitamin C test, confirmed it was iron staining and conducted the AA treatment. Was a complete success; all of the stains went away. Have been adding around a bottle of Jack's Purple Stuff about every 10 days. (half bottle on day 1 other half on day 5.) As part of the AA treatment, it was recommended to keep Ph levels on the low end - 7.2 or so. I'm now 4 weeks out from the AA treatment and everything seems to be holding well. Then I realized that the Ph was below the recommended level of 7.6 - 7.8 for a SWG, per pool school.

So, my question is - which is more important: keeping the Ph low (7.2) to prevent metal stains or keeping the Ph on the higher side (7.6 - 7.8) for the health of the SWG?

 

[pooldv]

7.2 is fine. My PH rises and I lower it to 7.2 regularly. SWG is 3 and doing great.

 

[woodyp]

I'd say metal stains wins that battle. The SWG is always gonna wanna drive up the PH all by itself btw.

 

[pooldv]

Just checked my SWG manual and it says 7.2 to 7.8.

 

[JoyfulNoise]

How often do you add acid to keep the pH at 7.2? What are your other water parameters?

Have you considered adding a water softener to your fill line to help mitigate the constant metal introduction? Some on this forum have recommended the Iron Curtain filtration system.


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[PoolESQ]

Joyful - I have the Autopilot total control system which includes an auto dosing acid pump. I don't know how much it adds, but I do hear the pump kicking on and off throughout the run time. I do have a water softener but the hose bibs are plumbed outside of the softener. I may have mistakenly understood that water softeners do not necessarily remove metals such as iron. I thought they required a special filter. The Iron Curtain system you linked to sounds fantastic! I will most definitely look into adding it line with the water softener.

My other parameters are (taken this morning):

FC: 7 (raised slightly in anticipation of pool party)
CC: 0.5
Ph: 7.2
TA: 70
CH: 300
CYA: 30 (purposely kept low so as to not interfere with the ORP probe readings)

 

[JoyfulNoise]

Joyful - I have the Autopilot total control system which includes an auto dosing acid pump. I don't know how much it adds, but I do hear the pump kicking on and off throughout the run time. I do have a water softener but the hose bibs are plumbed outside of the softener. I may have mistakenly understood that water softeners do not necessarily remove metals such as iron. I thought they required a special filter. The Iron Curtain system you linked to sounds fantastic! I will most definitely look into adding it line with the water softener.

My other parameters are (taken this morning):

FC: 7 (raised slightly in anticipation of pool party)
CC: 0.5
Ph: 7.2
TA: 70
CH: 300
CYA: 30 (purposely kept low so as to not interfere with the ORP probe readings)

Yeah, I was thinking there was no way you were maintaining a pH of 7.2 with manual acid additions

So your CSI is -0.57 approximately. While that says nothing about metal scaling, your water is definitely aggressive enough to keep any scale from forming on the SWG. I do understand why your CYA is so low given that the ORP probes have a hard time with stabilizer. However that does mean your SWCG is running pretty hard all the time to keep up with the chlorine demand from the UV. Hopefully you've got the oversized cell option. I considered getting the Pentair equivalent (IntelliChem) for our pool but decided I would wait a little bit longer. Given the ease with which my IntelliChlor operates and my fairly stable FC, I think the only things I would add in the future are a larger cell size (IC60) and, perhaps, and IntelliPH for acid dosing.

Anyway, I agree with the others, metal staining takes precedence here. I know nothing about the Iron Curtain, only relaying what I've seen others post. It would definitely be a custom install because, as you say, spigots are generally on their own loops from the city water main in most homes. A standard water softener doesn't do anything for iron, you definitely have to have one of these systems that are specialized for metal removal.

Good luck!!

 

[bkfamily1]

I had the plumber add a soft water line outside for the pool during a kitchen remodel. But that was to manage CH. Softeners help some with iron but that is not their primary purpose or function. I think high iron in your well may cause issues with your softener but I am not sure. My house originally had an iron filter in line before the softener when the well was new. But as the well matured it accumulated enough sediment to self-filter the iron and the level of iron in the water dropped (so said the softener company who said I did not need to replace the iron filter when it died).

You could also look at a filter that goes on the end of your hose when you are filling. Look for brands like MetalTrap, EcoOne and PreFresh. They are pretty cheap and last for a season or two. I have also seen cartridge filters for iron.

 

[PoolESQ]

Joyful - Having the total control system has definitely been a learning experience. Once I mastered it, I would not do without; but for a while there, I it was driving me nuts. The Ph probe works spot on. It has always perfectly matched with my TF-100 results. The ORP is a different story. First, there really is no standard ORP level to FC level correlation. In other words, an ORP reading of 600 does not always equal a FC level of 5, for example. So it does take some playing around before you are able to zero in on what the ORP reading of your water is relative to the FC level. (It may actually be TC that the ORP measures, I'm not positive about that.) In any event, things get more complicated when you add anything other than bleach or MA to the water. (I don't know about baking soda, because low Ph has never been an issue for me.) When I did my ascorbic acid treatment, for example, the ORP to FC correlation completely changed. Whereas previously ~600 ORP = 5 FC, after the AA treatment, 600 = 10 FC. So I had to lower my ORP to ~400 to get back to the FC 5 reading. So long as I don't add anything unusual to the pool, the ORP keeps things adjusted perfectly. But each time (fortunately those times are rare) I add something out of the ordinary, it throws the ORP reading off and I have to try to match the new ORP to FC levels.


bkfamily1 - It's funny you should mention, I did just purchase a MetalTrap hose filter. It should arrive in the next couple of days. It had better work - those things are not cheap!

 

[bkfamily1]

I guess I should have said "compared to a whole house iron filter like the Iron Curtain."

 

[PoolESQ]

Oh absolutely! I was just expecting the MetalTrap to be somewhat in line with other hose filters, in the $30-$50 range. I paid $150+shipping for mine.

 

[bkfamily1]

Honestly I am surprised also. I did not know that particular brand was so expensive. I thought they were all around 40 or 50. Is there something better about the MetalTrap?

 

[PoolESQ]

I'm having to rely on reviews for now, but I'll let you know in a couple of weeks how well it works. It does come highly recommended.

 

[JoyfulNoise]

Chemgeek has written extensively about ORP in this post.

Just to clarify, ORP doesn't measure FC directly, it measures the oxidation-reduction potential of the water. The ORP voltage is sensitive to the concentration of ALL oxidative species in water - hypochlorous acid, dissolved oxygen, peroxide, ozone, hydroxyl radicals, etc. it is also affected by pH, temperature, alkalinity, CYA and TDS. Fouling of the membrane in the ORP probe can also affect the measured voltage.

That is why when you say adding atypical chemicals to the water causes the ORP voltage to shift. Those chemicals either directly affect one of the oxidative species listed or the chemicals modifies the membrane in the ORP cell shifting the ORP voltage. It is also the reason why you have to keep your stabilizer so low - the CYA lowers the hypochlorous acid level (active chlorine) which is the thing you actually want to measure. If you add too much CYA you make the hypochlorous acid level so low that it introduces too much noise in the measurement and the other oxidative species are unaffected by the CYA.

ORP is pretty tricky but it seems you have made it work for you so congrats on that. I'll stick with my standard duty-cycle controlled SWG as my FC is pretty stable and predictable. Someday there will be acid injection in my future pool but that's a ways off.


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[PoolESQ]

 

[chem geek]

So, my question is - which is more important: keeping the Ph low (7.2) to prevent metal stains or keeping the Ph on the higher side (7.6 - 7.8) for the health of the SWG?

Your signature says "Sunstone Quartz Midnight Blue 16x32 rectangular gunite". In theory if you are using enough metal sequestrant than a higher pH won't cause restaining. You are apparently very worried about that but not worried about protecting your pool surface by saturating the water with calcium carbonate. Check back in with us in 5 or 10 years and let us know how that surface has held up.

 

[PoolESQ]

Chemgeek - that's why I'm asking these questions. I cannot get a clear opinion one way or the other. I read on here all the time re: Ph: anything in the 7s is fine. Then there are the specific recommendations depending on what pool type you have. And, as you can see above, everyone that has chimed in says, "you're ok." I went ahead and raised my Ph to 7.3. My CSI is now -.47, up from -.57 still within the acceptable range per pool math. There are also many posts I've read on here to keep ph low to keep metals from falling out of solution. So, I'm at a loss. I'm not sure why the snark about not being concerned with saturating calcium carbonate. I am obviously worried about the integrity of the pool as a whole, while trying to respond to the metal staining.

 

[chem geek]

Keeping the pH low to prevent metal staining is the approach that Ecosmarte uses to prevent copper used in their system from staining plaster surfaces. That is only one method. If one uses a metal sequestrant then it is supposed to bind to the metal even at higher pH.

I wasn't being snarky at you specifically and I'm sorry it sounded that way -- there are those on this forum that don't believe in or understand the science of saturating the water with calcium carbonate and the only way to show them the damage they may cause is to get reports back years from now of plaster surfaces that have followed CSI levels well below -0.3 (say -0.6 or lower). A CSI of -0.3 has HALF the level of calcium (or carbonate or their product) of full saturation while -0.6 is ONE-FOURTH full saturation level. Low pH is by far known to the the predominant factor in both metal corrosion and plaster deterioration.

 

[JoyfulNoise]

there are those on this forum that don't believe in or understand the science of saturating the water with calcium carbonate

If anyone wants or needs convincing of the science and practical effects of monitoring and controlling CSI, they are welcome to PM me anytime! My particular pool chemistry, which I believe is fairly representative of pools in the southwest and high CH-water areas, benefits greatly from close monitoring of CSI. The proof I can show is visual as well - I will show you what calcium scaling on pool tile looks like when you don't pay attention to CSI (but stay within "recommended ranges") and I will show you the same tile, completely scale-free by simply keeping a close eye on the CSI.

CSI is a real and important parameter, at least it is for me and my pool.

 

[PoolESQ]

Thanks Chemgeek for that explanation. I didn't understand why I upset you, and I do understand your frustration with those who don't listen. I am not among them. I also appreciate your advice that -0.3 CSI is much better than -0.6 by 100%. I thought that anything between -.06 and +.06 would not cause problems. I now stand corrected.