1. Do NOT turn the pump off till the pool is clear. (Why did you do that?)

2. What is "rapid shock"? Don't use it, till you've posted EXACT chemical name and BRAND name. Use bleach!

3. It sounds like you have a filtration problem, not an algae or chemistry problem. Post the EXACT model of your filter and pump (get the PUMP model, not the MOTOR model. Pump model number will be on the wet end of things, not on the motor.)

In most cases, a 2 HP pump is way, way too large for an AG pool sand filter. You may well simply be forcing the dirt through the filter!