The green stuff is just alge & as long as its not all over the roots it wont hurt anything at all,no need to use anything other than cold clean water to cleans it.
If doing hydro & it gets on the roots in heavy sections of roots it will slow nutrient uptake,ya just rinse it off in the shower & she's as good as new.
Every once in a while i get alge exactly like that on the plants i have in veg,its from too much light comming in contact with areas that have fertilizer on the surface area,the alge eats the fertilizer,its no big deal at all & many growers deal with it on a regular basis.