Yes, Pool Magnet is a sequestering agent. It will bind with metals in the water to hold them in suspension. Yes, they are expensive. You can find them cheaper on the web sometimes. Unfortunately I don't know of any "homemade" sequestering agents After a while you will get to know how to work your own pool. The important thing to remember is high ph along with high chlorine will make any metals that are not sequestered fall out. What I usually do is add a little sequestering agent (about 2 oz) a week (if I remember), and watch for stains (with this expression If I see them start, I lower the ph down to 7 and add a little more sequestering agent (about 8 oz.) and let it circulate. It usually removes the new stains. Sequestering agent breaks down, and is lost, so it does need to be replaced, and it is expensive, but keeping on top of it, by watching the ph and keeping the chlorine up to good levels so you don't have to shock, makes the process less painful