Are you brushing the pool while the chlorine level is high? I'd continue to keep the high level while you are trying to clear it. One problem you are likely to have is that your pump is way overkill for your pool. We see that alot on AG pools. When your pump is too big, it can simply force debris through the sand field without actually filtering. Keep your pump running 24/7 while you are trying to clear it. Chlorine will kill the algae but you have to give your filter time to try and clear it out.

You also might want to verify that your sand filter is working by doing the DE test.
http://pool9.net/de-test/