Now that you're getting very little brownish stuff on your filter, I believe you can go ahead and shock your pool.

You need to understand that high chlorine levels along with high pH levels will cause the metals to turn your water brown again if there's not enough sequestrant. So...you need to keep your pH on the low side--7.2 is ideal. I would go ahead and add your bleach, starting with what you have been adding to target about 5 ppm. If the water stays clear for another hour or so after that, add some more, maybe enough to go up by another 3 ppm. If it still stays clear, then go on up to 12 ppm. That is shock level, assuming you have less than 20 ppm of CYA in the water. If you can get it to 12 ppm, then you want to hold it there until you're losing less than 1 ppm of chlorine when testing after the sun is off the pool and again before the sun hits the pool in the morning. This, combined with 24/7 filtering with frequent washing of cartridges, should clear your pool up the rest of the way. I would add your chlorine at or just in front of the skimmer, so that if it's going to cause the iron to fall out, hopefully it will do so on your filter so it can be washed out and removed. If at any time during the raising of the chlorine the water starts to turn brown again, add another dose of metal sequestrant.

I want to reiterate that I'm NOT the resident metals expert, but from all the reading I've done of Mbar and Pooldoc's post, this is the route I would take with my own pool if I were in your shoes. I'll see if Ben can stop by and offer more useful information, but in the meantime, that's the plan of attack I would use.

Janet