I have never even heard of a sequestering test kit - but there are a lot of things I have never heard of I do know however, that Jack's Magic tends to use more product than is really needed. I would suggest buying some - and just watch for stains - when you see some forming, take your ph down to 7, and add 1/2 bottle. I don't do a matainence dose, I just watch - sometimes even just taking your ph down will lightnen the stains. You will get your own routine down after a while. I always keep some ascorbic acid on hand too - this way if the sequestering agent and low ph don't work on the stain, I add a little ascorbic right down the side where the stains are noticeable and let the water circulate - most of the time there isn't much chemistry change. Just make sure you keep your ph at 7 - 7.4 with a fiberglass pool - I find with my pool, when the ph gets above 7.6 I start to see stain. Hope this helps - I am sure Jack's Magic really knows about stains - and can get you to keep a stain free pool, but it does get to be expensive using all that "purple stuff", when it may not be needed.