A1. If you are algae free, and not seeing metals, you don't have to use the polyquat. However, using small doses of it will help filter out iron particles that may form, because it's a very effective filter aid.

A2. Make 100% sure your feeder is empty. Then, check again. Use borax to gradually raise your pH to 7.8, while continuing to chlorinate. Once your pH is 7.8, begin adding 1/2 lb doses of calcium hypochlorite DIRECTLY to your skimmer, while the pump is on. This 'shocks' the water in the line upstream of the filter, and tends to drop iron out ON your filter. Continuing to use DE during this process will also help pick up remaining iron. Make sure your pump is on 24/7

A3. Avoid shocking the pool for time being, except as noted above.

A4. Stop using a sequestrant. You do not want to KEEP the iron in the water; you want to get it OUT on your filter (per #2 above).

A5. It would be a good idea, till you're pretty sure the iron is gone.

A6. Go to http://pool9.net/borates/