How often do I clean out the reservoir
 

Average problem. How often do I clean out the reservoir, what do you clean it with. Is there any chemical or item that you add to the nutrient solution to keep green slime out of the system. Have been growing for a year.

About every couple months clean the reservoir with a ten percent bleach to 90 percent water solution.
And if you don't have green slime in you system then your nutrient solution isn't right. You can't grow hydroponicly without green slime. Some systems more than others depending on how well you can keep light from hitting any water in your system.