Clearex is a solution for flushing and cleaning out salt buildup that nutrients leave behind. When I flush biweekly, I drain my reservoir of all nutrient solution and add pure reverse osmosis water plus 15ml per gallon of Clearex. When I'm filling the reservoir, I make sure to wash down the roots and sides of the res. with the flushing solution. I let the bubbler system run for about an hour with the clearing solution, then drain. I then refill with new, fresh nutrient solution. The plants seem to respond very well. If you don't flush, you'll begin to see salt buildup on your hydroton as well as the sides of the res. The plants are certainly retaining these salts as well, which over time will begin to dry them out, cause nutrient lockout, and will lead to their demise. I also plan to run only Clearex soultion for the final 3 days before harvest. This allows the plants to flush out any salts and use up any nutrients stored in the stems, leaves, and buds, leaving a clean, pure plant.