I'd get some bleach in it. The Sun will burn it off rapidly in the day, so I'd put it in at dusk.

Slosh it around as you put it in to prevent it from really concentrating and then it will disperse naturally. I little submersible pump, if you have it, may be of some assistance. It will be gone soon after the Sun hits it so you'll need to add it each evening to be really effective. Use the bleachcalc to tell you how much.

Soon, you'll be able to get some CYA in there but I don't think I'd try it 'til you get at least a foot or more of water.