Be VERY careful with the power washer and use it on the lowest setting. I've seen mine actually strip the stain and even rip wood off my cedar fencing and decking--you do NOT want to damage your finish! Personally, I'd rather see you brush the pool with a pool brush.

When you refill, Tri-Chlor tabs and Di-Chlor powder WILL add CYA to your water--Di-chlor will add both chlorine and CYA faster than the Tri-chlor tabs.

Someone correct me if I'm wrong, but I think 1 lb of Di-chlor SHOULD give you an initial FC of about 6.6ppm to 10,000 gallons of water. (which means roughly 6ppm of CYA). I'm basing this on Chem_Geek's post that 24.1 oz of Di-Chlor will add 10ppm of FC to 10,000 gallons.

http://www.poolforum.com/pf2/showthr...ight=chem_geek