Epsom salts provide both magnesium (Mg) and sulfate (SO4, an ester or salt of sulfuric acid) in a gentle form that is easy for Cannabis plants to process – one that does not build up in soil over time. This home remedy is also simple to use, inexpensive and a highly-soluble supplement for...
You are flushing which means that you want to saturate the soil so that the plants take up all of the nutrients left in the soil.
If you were growing in hydro all you would have to do is flush with water only for 3 or 4 days.