Step 1: Triple shock water to 30 PPM with Sodium Hypochlorite Liquid Chlorine (you can use other types of chlorine, it's just that the liquid will probably be easier).

Step 2: Thoroughly clean and brush. If you have lots of debris and algae, remove as much of it as you can with a screen.  This will take some of the burden off of the filter.  Run pump and filter continuously for 24 hours or UNTIL THE WATER IS CRYSTAL CLEAR.  If the pool is real bad you may have to clean the filter SEVERAL times.

Step 3: Test all water factors and balance water.  If chlorine level is still high, just balance the other factors.

Step 4: Test water every 24 hours for 7 days. Add chemicals as necessary to keep water balanced.  Don't use the pool or spa until all factors are Perfect.

Step 5: After 7 days follow basic routine maintenance schedule.