I was in the same boat as you and have tried just about everything... My CYA is higher than yours (100) and here is what I have done with the best results. (Dumping water was not an option)

If your water is clear, stop feeding chlorine and let the levels come down to 1 ppm or so. For your amount of water, get about 2 lbs of ascorbic acid and two bottles of ProTeam Metal Magic. When the chlorine drops, bring the pH up to around 7.6-7.8. With the pH correct, add the ascorbic acid it the skimmer. Let the acid circulate for a couple of hours or until the stains have disappeared. When the stains are gone, add two bottles of Metal Magic. Wait 24 hours and then start to bring the chlorine up. Do not add any shock or liquid chlorine. If you have a feeder, put it on its lowest setting. If you put tabs in the skimmer, just keep an eye on your chlorine levels. You do not want to go higher than 2-3 ppm. If you have high metals, every week, you will need to add metal magic.

I have been fighting this all summer and so far this has been the best. The ascorbic is expensive but the Metal Magic is $17 at my local store. I feel somewhat stupid because I am a water engineer and this has been the hardest thing to deal with.

Give it a try and let me know how it goes.

Regards,
Chris