You need to maintain that shock level (15 ppm) until the water is clear, your CC is zero, and most importantly, you're not losing any chlorine when you test at sundown and again before the sun hits the pool. If you let the chlorine drop before you're at that point, then you have just wasted your bleach and efforts and not killed all the algae. AFTER those conditions are met, then you can go ahead and put the cover on it--most people shock theirs (which is what you have done) before closing anyway.
Since I never close my pool, I'll let the others advise you there, but take a look through the Fall preparation forum, especially this sticky http://www.poolforum.com/pf2/showthread.php?t=5720 for some guidance in closing it.
Janet
Incidentally, when you open again in the spring, I would highly encourage you to consider leaving out the mineral pack and just using bleach--the mineral pack adds copper, which is what stains hair and fingernails (and pool liners) if the level gets high enough...........
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