Thanks for the info Mike. We did try chlorine only. Kept the level at 15/higher for over a week with the pump running 24/7 (it's still on)..swept every day, then vacuumed to waste or ran the Dolphin about every other day. Although it did clear the algae up, it isn't enough to completely remove it, so we are going to the algaecide as a last resort. We only use the polyquat kind to keep gunking to a minimum. As of this morning this is where we stand:

16k gal IG Vinyl
FC 16
CC 0
PH 7.4
Alk 180
CYA 20