Not sure why you are having to backwash -- is the water still green?

Regardless, do this:

1. Add daily 2 gallons of PLAIN household 8% bleach to the pool, for each 10,000 gallons. Add the bleach in the late evening.

2. Purchase a cheap OTO test kit (yellow / red drops) and test the chlorine level in the AM, after dosing the night before. Test the pH & chlorine again in the PM. Post results here.

3. Tell us about your pool: size, gallons, type of filter.