I have a 10K fiberglass pool that has iron stains. Although Ascorbic acid works great it makes it difficult to manage the chlorine levels (even with the Hayward SWG). I want to try the stain removal process described in the sticky on the forum but it mentions using Jacks Magic Pink Stuff. After I ordered that I noticed printed on the back of the bottle it states that for salt water pools Jacks Magic Purple Stuff should be used. Is that correct?