Well one way or the other, if you do now cover you res. with something.....
you will have continuous algea. COVER UP YOUR SHIT PLAYA!! do something figure it out. Also while your figureing things out take all your equipment and wash them well with boiling hot water... then proceed to scrub the shit out of it. Try to add new ph'd and nutirent added water to your res atleast once a week. Maintenance is an important part of any horticulture grow but especially on dro my friend

Peace,
Cptweedmanguy