Within Ben's 'sticky' he recommends "drain and refill .... If you don't drain, plan to consume a LOT of chlorine, getting rid of the ammonia and urea....."

If you had high CYA levels (> 70 ppm) last fall, you may consume as much as 200 ppm of chlorine in the clean up process. (~ 80 gallons of household bleach, for a 20,000 gallon pool!) "

Draining / refilling might be cheaper than chemicals depending on where you live. ( just be safe in draining).

Good luck.