Use a little muriatic acid to lower your pH some. Add about a pint slowly in front of a return jet -- gloves, glasses, stay upwind of fumes, pour very close to the water to avoid splashing. After a few hours, retest pH and repeat til you get below 7.8.

You need to shock your pool back up to 15. Also, run the pump 24/7 to let the filter trap the dead algae. Test your cl in the evening after sundown and then again in the morning within 2 hours of sunup and see if you are losing more than 1ppm of cl overnight. If not, your algae is dead and now it is time to be patient and let the filter do its job. (Don't test your pH when the chlorine is high, however, or you'll get a false high reading.)

You might try adding a little DE to your filter. Many of us with sand filters do this to help it filter a little better. More about that here:

http://www.poolforum.com/pf2/showthread.php?t=3742