If you plan to drain and refill some water, go ahead and do that firt. Then test for CYA again and shock based on the chart and new level. The key to killing it all, though, is to sustain that shock level until the pool is blue and clear-- and until you dont lose anh chlorine from sundown to sunup. To keep your CYA down, use bleach or cal hypo for chlorination--no trichlor or dichlor.

Janet