At an 8.5 pH, the rinse water is very alkaline, and needs to be balanced out before using. Most of the hydroponic books will say that changing the water and rinsing the unit every 2 weeks to a month is important, but you really don’t have to listen to the instruction manuals. Even then, some growers just rinse as a safety precaution. When the unit is drained of its water, there will only be a negligible amount of nutrients left. This doesn’t have much effect on the nutrient or pH levels of the new nutrient-water solution. It is, however, prudent to rinse and sterilize the units between crops.