How much molasses to add to the flush water? I’m at week 9 with autoflowering plants almost ready to harvest.
Idk. I always flush with pHd water
Welcome to the community. I have not heard of adding molasses to flush water. Maybe someone with more grows under there belt could chime in. I flush with water like GhostGrow. hopes this helps? happy growing 
Low sulfur molasses has been added to living soils to help the biome but is not directly helpful to the plant. There is really no data to support it doing anything at all. If in hydro you want to use nothing organic either. In soil or media you should be okay and won’t hurt plants but really is a waste of time in most cases. Flush with low TDS water and monitor runoff.
what PH do you go for when flushing?
I have been using well water adjusted to a pH of just under 7.