Just entered your pool info, and turned on your signature. I based the gallon calculation on 3.5' water depth, and on the break (transition to deep end) occurring 18' from the shallow end. Add 1200 gallons if it's actually 4' deep water.

Going back over the thread:

1. If you are going to drain and refill, do NOT add borates or phosphate removers until you have refilled.

2. Most likely 16,000 gallons of your water are in the top 3.5 feet. If you drain 3.5' of water, and refill, you'll probably lower your CYA from 130 to about 40 ppm.