gotta cut out the light. maybe stick some mylar over your pots and rocks in your ebb n flow. dont want clear tubing in the system. as long as your res is not receiving any light you should be good.

i dont use a cover on my res. but did get a lot of algae in my drip systems because my tubs were white and light went right into them. covered tubs in dark plastic and put mylar on top of my baskets to prevent light hitting them. still have clear tubing with algae growing in them but doesn't seem to be spreading. tho they do need changing. system stays pretty clean now.