Perimeter Stain

[edarling]

I thought the sequestering agent put the metal in suspension so it can be filtered out. So, if you raise CL too soon, the metal falls on the liner and stains, but if you wait a week or so, the stuff filters out of the water. No?

[mbar]

I thought they would be filtered out too, but I am told that they do not get filtered out - they just stay in suspension. But I have had my water tested after the treatments and they test as no metals, so I don't really know. I do know that if I keep my water treated with the sequestering agent I don't get the stains back. I keep reading all I can about the metals in swimming pools, but there doesn't seem to be a way to filter the metals out, except by doing it a way that Pool Doc says - but it involves careful control of ph and bleach to get the metals to fall out on the filter. I don't have a complete understanding of it yet. If anyone out there can chime in and give a better answer, please do!

[NWMNMom]

Don't know about a better answer, but I do know that when we had the well pump filters breached while filling, our pool turned chocolate brown - I mean really brown. We made the mistake of putting the bleach in the water (not knowing that the filters had been breached) so when we put the first sequestering agent in the NASTY stuff made a 2" wide ring of crap around the perimeter - this brand of stuff apparently had the phosphonic(sp?) acid along with "soy protein" or some such junk in there as it was claimed to help "soften" the water. Horse Pucky - it just made a mess around the edges of the pool. The Metal Myte (good stuff) sequestering agent went in and we ran a cartridge filter and a small sand filter 24/7, cleaning and backwashing often - there was sticky thick goop on the cartridge filter and brown ooze came out of the sand filter when backwashed. We had to use a LOT of the Metal Myte - at least 4-5 bottles over a week. The water is now clear and does not test for metals anymore. There is a thick puddle of brownish orange residue on the ground near the edge of the woods where we cleaned cartridges and backwashed the old sand filter to attest to something being removed from the pool. My guess is if it puts it in suspension, it must coat the iron/metal particles and they can then "stick" in the filter better? Kind of like what the clarifiers do, make it clump? It took something out of the pool.

[waterbear]

CHEMISTY NERD STUFF ALERT! NOT FOR YUPPIES OR THE WEAK OF HEART!

I thought they would be filtered out too, but I am told that they do not get filtered out - they just stay in suspension.
Right Marie!, They are still in the water but in a 'chelated' form that keeps them from reacting with other chemicals like the chlorine or falling out of solution as stains. That is why it is important to keep up the maintenance doses of sequesterants if you have a metal problem.
But I have had my water tested after the treatments and they test as no metals, so I don't really know.
The metal ions are "seqeustered" (from dictionary.com)
se·ques·ter
v. se·ques·tered, se·ques·ter·ing, se·ques·ters
v. tr.

1. To cause to withdraw into seclusion.
2. To remove or set apart; segregate. See Synonyms at isolate.

The metal ions are, in effect, 'set apart' or inactivated by a process called 'chelation'

once again from dictonary.com
Chemistry. To combine (a metal ion) with a chemical compound to form a ring.
This ring structure means that there are no reactive points that can be affected by other chemicals in the water as long as the metal stays in this ring structure.
This is an oversimplification but you really do have a good understanding of the process and are the 'metal guru' of the forum!
Practical knowledge is MUCH MORE useful than the theoretical and you have that down!
I do know that if I keep my water treated with the sequestering agent I don't get the stains back. I keep reading all I can about the metals in swimming pools, but there doesn't seem to be a way to filter the metals out, except by doing it a way that Pool Doc says - but it involves careful control of ph and bleach to get the metals to fall out on the filter.
You are causing the metals to drop out of the ring structure and then fall out as stain on the filter by carefully controlling the parameters that break the chelation of the metal in a controlled way. It is tricky and doesn't always work right. PoolDoc understands this process much better than I do!
I don't have a complete understanding of it yet. If anyone out there can chime in and give a better answer, please do!

Hope I explained it a bit!
As a side note that might help, I have used copper in fish tanks to treat certain parasites. Copper is available as chelated or not. If you use chelated copper it doesn't show up on a test until it breaks away from the chelation. I have seen tanks that all of a sudden would test at high levels of copper a month or more after treating with chelated copper and showed practically no copper from the time of treatment until then. If the treatment with the chelated copper is overdosed it can prove deadly to some of the tank livestock when it becomes active and the copper levels shoot up and overdosing is easy because the copper doesn't show up in full concentration on testing in chelated form. I know that many copper based swimming pool algecides use chelated copper which WILL eventually cause staining down the line for the same reason.

[mbar]

Thanks Waterbear! Last year I played around a lot with the water in my pool to see what would stain, and what wouldn't - I ran high ph with low chlorine, ran high ph with high chlorine, ran low ph with high chlorine, and low ph with low chlorine. I started the year with low cya, so I was able to do these tests along during the time I was raising my cya with trichlor pucks. I used very little sequestering agent, to see what happened after ascorbic acid treatments, verses using just the sequestering agent with low ph to take the stain away. Now this year I am trying to do the whole summer without stains. So far, I have been able to open it and be almost stain free - I noticed a little stain forming on my seats, so I brought the ph down and added more sequestering agent - the stains lightened up. I put 3 bottles of Sequasol in so far. My pool is perfectly clear, and stain free (yeah) This year my cya didn't disappear, so I started with a cya of 35 - I am using almost all bleach - I do put a puck in the skimmer whenever I add water, and whenever I take my chlorine high. So far so good, but I am not counting my chickens, because in past experiments those nasty little brown stains came back to taunt me! I have some other theory's too - but nothing I can say for sure. I will keep trying and hopefully we can all learn from each other - that's why it is so great when others post their results here. Thanks again Evan, you really explain the chemistry in a way I can understand it.

[waterbear]

Marie,
Very glad to hear it was helpful!