With the SWCG on, it is better not to cover the are of the return jets, so as to allow the hydrogen generated by the cell to dissipate. The CYA at 70 ppm should be enough to keep chlorine without the pool cover.

By all means backwash to waste. You appear to be winning the algae battle, and as the FC starts to drop less and less, then is the time bring the FC level down gradually, at about 5 ppm per week. If you start to see algae again, bring it back up to 15 ppm and hold it until it goes. Again patience and perseverance is needed.

Pat