I agree with dmanb2b, your CYA may be well above 100, can you try diluting your pool water 1 to 1 with distilled (maybe even tap) and test the dilute sample for CYA, if it's still 100, dilute 2 to 1 etc. until you get a reading within the range of the test. The accuracy of this testing will be lower but you'll have a target for the partial drain / refill you'll need. There are some postings on this forum that describe using a plastic membrane to fill while draining without risking the integrity of your pool or wasting fill water.