Hi Paulette. That can depend on the stains -- there is a way to test. Here's the link:
http://www.proteampoolcare.com/images/uploads/MetalMagicSpongeTest.pdf
Metal Magic is just a sequestrant, which you have to use during an AA treatment anyway. But in your case with SWG, you might be better off using Jack's Magic Purple because its formulated to work with SWG and has a cell cleaner in it.
Generally, TFP has found the AA treatment to be the most reliable/surefire method of stain removal, which is why its the recommended treatment. But sometimes people have trouble having the FC so low, end up with algae, and end up having to shock...which then might bring the stain back. Or alternately, they can bring FC back up too fast, which can also sometimes have stain come back.
A few seasons back a poster on this forum who didn't like doing the AA treatment shared that he tried just using the large dose (after doing the sponge test) and for him it worked just as well. So I tried it, because it was a bit easier (not necessarily cheaper) than AA. It worked great for me. I'm vinyl with a sand filter and lower calcium. For people with higher calcium, it can cloud for a day or two while working.
However, I wasn't SWG at the time (just switched) and large amounts of any HEDP metal sequestrant do break down into orthophosphates eventually -- which normally doesn't present any actual issue, but some SWG manufacturers like Pentair refer to water balance guidelines that include lower phosphate levels (Hayward doesn't.)
Most of the phosphate talk by pool stores is garbage for those who know TFP...how to test their water and maintain FC to the CYA ratio as shown in the link in my signature
But there has been some research in the boiler industry, where the same sequestrants are relied on heavily, that suggests orthophosphate in really high levels can scale, especially if calcium is high.
Are you on well water? Are you already using a metal sequestrant? How bad is your staining? And do you know if its iron, or copper?
If you've not just tried using a sequestrant alone, you might want to do that first (eg Jacks Magic Purple) to see if you actually need to do the AA or not. Maybe something like the same sponge test would work to give you an idea if Jack's will have the same effect stain-wise.
Over the last few seasons, I've also called the tech line at both proteam and Jacks on different occasions and gotten helpful information. If you want to try Metal Magic, you coud check first with them to see if it works the same way in a saltwater pool.
Good luck with the stains whichever way you go!
Here's the original thread. Note that both RaveJim and I had regular chlorine pools at the time of experiment, not SWG:
Switching Sequestrate from EDTA to HEDP - Page 2
