Adding Sequestrant with high FC---what's the drawback?

[gilbee]

Because it's easy with my SWG, I've kept my FC rather high all summer (7-9FC with 60-70CYA), figuring it would give me a buffer for high bather usage, or if there's a problem with the SWG while I'm away on business trips.

I'm noticing metal staining which I suspect is due to the high FC paired with the occasional rise in pH over 8 when I'm not home to deal with it (new plaster this year). Well, that the metal staining is showing because of it...not sure where the metal is coming from (I've got an old gas heater, and the water did turn clear green when they filled after the replaster; I didn't realize I needed to keep adding sequestrant after that initial dosage the plaster contractor added. I've confirmed that the stains I have are metal via vitamin C tablets, and have bought a couple bottles of Jack's Purple stuff...with my FC at 7, what would happen if I just added it now instead of trying to lower FC first? I'm only home for this week, and then I leave again for 2-3 weeks, so I definitely don't want to try to lower FC and then leave the pool in a position to let algae set in with no one watching it close. Even now with lower temps, we get a LOT of leaves, and unless I'm home they will sit for a day or two before my lovely wife will get them out, further scaring me from dropping the FC.

While I understand that there is a potential for reduced effectiveness of the product at higher and near-zero FC levels, what exactly occurs? Does it reduce the FC (thus lowering FC instead of sequestering metal), or does the FC kill off the sequestrant entirely in some way? Will tossing it in now be a complete waste of money, or might there be some benefit to it, though less than optimal? If there is benefit (though reduced), I'm inclined to toss it in now and continue the effort when I return, but if not, I'm thinking I'm better off just waiting a few more weeks.

 

[chem geek]

Chlorine slowly breaks down metal sequestrants. When that happens, the metal that was bound to the sequestrant gets released back into the water and can potentially stain. This is why one must maintain a maintenance dose of metal sequestrant. If you run at a higher FC/CYA level then you'll need to add more metal sequestrant over time to maintain its level. Ideally, you can measure the sequestrant level to know when and how much to dose -- ask Jack's if there's a test for the Purple stuff. If not, then ask them what they think of the rate of degradation though I doubt they know, especially with the chlorine/CYA relationship they probably don't understand in detail.

 

[JoyfulNoise]

Interesting information HERE. Looks like Jacks and LaMotte both sell a test.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[gilbee]

Interesting information HERE. Looks like Jacks and LaMotte both sell a test.

Thanks---Also of note from that post:

"Jack's said that Blue/Pink/Purple Stuff can withstand around 10 ppm of Free Chlorine (FC) for a short period of time, but higher FC levels, or longer periods of time, will "consume" the HEDP. If there are sequestered metals still in the water, they will be released back into the water."

- - - Updated - - -

Chlorine slowly breaks down metal sequestrants. When that happens, the metal that was bound to the sequestrant gets released back into the water and can potentially stain. This is why one must maintain a maintenance dose of metal sequestrant. If you run at a higher FC/CYA level then you'll need to add more metal sequestrant over time to maintain its level. Ideally, you can measure the sequestrant level to know when and how much to dose -- ask Jack's if there's a test for the Purple stuff. If not, then ask them what they think of the rate of degradation though I doubt they know, especially with the chlorine/CYA relationship they probably don't understand in detail.

So if I wanted to be sloppy but still have a shot at doing some good over the next couple of weeks, I could simply add more than what the bottle calls for, right? I think the sequestrant test kit might be the ticket, but I don't think I can get that and formulate a plan before I head back to work.

 

[JoyfulNoise]

Other than aesthetics, is there some reason you're rushing this?

What you really want to do is have enough time to perform a proper ascorbic acid treatment (to dissolve the metal stains into the water) and then use the proper amount of sequestrant to keep the metals in solution. That requires a good deal of time but it can be very successful. There's also the MetalMagic products for removing stains that seem to work at higher pH values and is a little less involved than an AA treatment.

User swampwoman is someone you should PM about metals.

 

[gilbee]

Other than aesthetics, is there some reason you're rushing this?

I was under the impression that the problem would get worse...I didn't notice the discoloration until after I got back from my last trip where I was gone for a month...I don't know if it was actually that it got worse, or if just being away and not seeing it for a month made it apparent. That was kinda part of my question too---am I better off just waiting, or will the harm in not reacting to it now result in something that might be harder/impossible to rectify a few weeks from now? Sounds like maybe I'm better off waiting.

As for the AA treatment, I was gonna forego it and just apply sequestrant/purple stuff and see where it got me...I don't have a good way to isolate my heater from the plumbing at present, and I'm concerned that doing an AA treatment might push the heater over the edge into death based on its age...

 

[JoyfulNoise]

I'm no expert on metals by any stretch but I think adding Jacks without first doing an AA treatment is going to be a waste of time and money. Sequestrant by itself will only very slowly attack the stains. AA by contrast works in conjunction with the lowered pH to really etch away the metal stains. AA however only weakly chelates the metal ions and will degrade quickly from exposure to chlorine so you use a stronger sequestrant (HEDP) to hold the metal ions in solution when you raise the FC back up. So you really need both processes or you're just wasting your time.

As for aging, Fe stains are ok even when old. Cu stains are harder to remove with age but we're talking about years of aging here not weeks. You'd be better off tackling your metal issues when you have time to focus on it rather than hitting it willy-nilly with chemicals and "hoping" something works. The "dump & pray" methodology is what pool stores teach, not what we recommend.


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[JoyfulNoise]

Also, if the AA treatment poses a problem with the heater, then look into the ProTeam MetalMagic process. It supposedly does not require you to lower your pH and is a single step treatment. The only issue is I'm not sure it's designed for plaster pool or you might need a particular product AND it works by creating a lot of precipitated metal in solution so you need to baby-sit your filter and backwash it a lot.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[gilbee]

Also, if the AA treatment poses a problem with the heater, then look into the ProTeam MetalMagic process. It supposedly does not require you to lower your pH and is a single step treatment. The only issue is I'm not sure it's designed for plaster pool or you might need a particular product AND it works by creating a lot of precipitated metal in solution so you need to baby-sit your filter and backwash it a lot.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

Maybe I should take this time to replace my heater anyway...I've noticed moisture underneath it, and the water block where water enters/exits the unit stays a little wet as of a few weeks ago. It's 15 years old, and may very well be a contributing factor to the metals ending up in the water. I could take that opportunity to plumb in an isolation circuit so I can remove the heater for situations just like this going forward.

 

[smforte]

My experience with AA treatments (and I've done a few) have been great. Last time I forgot to test my FC which was at 6 the day before. The AA took it down to 0. I have a hard time maintaining the suquestrant and the stains just keep coming back.

 

[JoyfulNoise]

Maybe I should take this time to replace my heater anyway...I've noticed moisture underneath it, and the water block where water enters/exits the unit stays a little wet as of a few weeks ago. It's 15 years old, and may very well be a contributing factor to the metals ending up in the water. I could take that opportunity to plumb in an isolation circuit so I can remove the heater for situations just like this going forward.

If you do replace it, I would suggest you look into models with titanium heat exchangers. Those are the best and are resistant to chemical attack at normal pool pH levels. Cupronickel alloys are second-best but much better than standard copper heat exchangers.

A bypass loop with isolation valves is a great idea if you have the room for it.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[gilbee]

If you do replace it, I would suggest you look into models with titanium heat exchangers. Those are the best and are resistant to chemical attack at normal pool pH levels. Cupronickel alloys are second-best but much better than standard copper heat exchangers.

A bypass loop with isolation valves is a great idea if you have the room for it.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

I didn't know about titanium exchanger models...didn't realize such a creature existed. I ordered a rheem/raypak cupro-nickel based on forum observations, should be here by end of week. Doesn't matter now, but who makes a titanium model?

Edit: nevermind, I see that rheem and hayward make them, but it appears that they are heat pumps instead of gas fired heaters like what I have/bought. Also, I replaced with a similarly sized 400k BTU unit, which doesn't seem to be available with the titanium exchanger offerings.

 

[JoyfulNoise]

[EDIT]
My original statement -

Pentair makes a "commercial" model gas MasterTemp that has a titanium heat exchanger. Most manufacturers do.

is incorrect. The "HD" MasterTemp model by Pentair has it's heat-exchanger made from cupronickel alloy, not titanium. I was mistaken in my recollection from researching heaters long ago. Many thanks to TFP Expert JamesW for catching that mistake.
[END-EDIT]

Cupronickel is fine too. Much better than straight copper so you're in a good position. Add on a bypass loop and you're system will be top-flight.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[Swampwoman]

Hi Gilbee!
I am not on TFP as much during winter since my pool is closed A fair-weather poster, I guess you could say.

I am on well and have used various products and AA treatments to control iron. However, I am not on SWG, which I believe makes a difference in product use to ultimately avoid possible phosphate scaling of the cell plate (with extreme use, that is.) That's why jack's has a product specifically formulated for SWG, which is what you are using.

Because you're now presumably bypassing heater, AA is going to be most effective stain removal treatment if your staining is substantial. But some people have trouble coming out of the AA treatment and getting their FC back up fast enough without staining. The problem is if they develop algae, then shock, they kinda undo both the sequestrant effect plus the normal oxidization of metal and end up back at square one. That's why I originally changed over to mega-dose of Metal Magic using the sponge test, which will remove stains. Just not sure if its suited to SWG.

So had I been around back when you were headed out of town, I might have suggested that increasing the Jack's magenta to account for your higher -- but not over 10 -- FC would at the very least prevent additional staining, if not removed the existing stain. But I would have also suggested calling Jack's techs for confirmation of this approach -- both Jack's and Metal Magic techs have been helpful to me when I've called in the past

That said, both will cite their published parameters so, fwiw, I find that sequestrant will continue to sequester even if I'm riding 7ish on FC..I used to just dose more frequently. But I avoid slamming, as I know it will eat the sequestrant residuals and quite possibly release the sequestered iron

That said, if you're not on well and if the metal staining is indeed coming from your heater, you may not have to worry about the long-range planning and a single AA treatment with modest sequestrant followup may do the trick.

In my case, ultimately, I have switched to softened water spigot for refilling the pool to get the iron closer to non-staining range, and while it took a good season to do so, if you're on well I highly recommend this strategy with the note that if your surface requires higher calcium you may need to supplement with same.

Best wishes for a stain free, trouble free pool!