If your heat exchanger is not leaking, you don't need to repair it. The copper corrosion will stop as soon as your pool chemistry is OK.

Since you don't have a Taylor 2006 yet, add some polyquat (info at www.poolsolutions.com/gd/polyquat.html). Without the Taylor kit, you can't run the chlorine levels you need with a CYA = 120.

See if you can angle one of your return eyeballs to 'ruffle' the water -- it will help you gradually lower the alkalinity. Keep your pH above 7.4 and below 8.0, but use borax to raise and muriatic acid to lower it.

Order a Taylor K2006 or 2006C. You can use the Amazon links in my sig if you like, but as of this morning, you'll need to get the K2006C (2oz bottles), since the reliable seller (Amato Ind) seems to be out of K2006 (0.75 oz bottles) at the moment. Some of the other Amazon sellers (not sure which ones ) mix up the K2005 & K2006.