You're doing fine--now it's just a matter of maintaining that shock level over 12-15 ppm until you're no longer losing chlorine overnight. Keep the filter running as much as possible, preferably 24/7, to clear out the dead algae that's causing the cloudiness. Watch your pressure, and backwash the filter when it gets to 6-8 psi over "clean". If you don't notice your filter pressure rising, then you might try the DE trick that my co-mods use on their sand filters, where you put a cupful of DE in through the skimmer (just enough to raise your filter pressure by 1 psi) to help coat the sand and help it filter out smaller particles. You've got the right idea--now it's just going to take some persistence, some time, and some bleach