With a CYA of 70, according to the PoolSolutions Best Guess Chlorine Chart you need to get to 20+ ppm to get to a shock level.
http://www.poolsolutions.com/gd/best...e-chart.html#a
With the condition of your water, I would get it up to 30 ppm and leave it there until the green is gone. You don't want to let the levels drift down because the algae will bounce back. The water will go cloudy before clear but keep the chlorine at a shock level until it is clear.
It will take a a lot of chlorine, buy in bulk and pound the water. Better to err on the side of caution. Don't worry about PH at this time, because the high chlorine level will result in bad PH ratings.
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