It's Algae. It's A Living Plant That Will Eat & Suck Your Plants To Death. I Know I Just Lost 3 White Widows. It's From To Much Light Getting To The Resevior & Warm Water! Block All Light I Mean ALL Light! I Painted Mine Black 3 Coats Before I Could See No Light. Change Your Clear Tubing For Black. Put Covers Over Your Net Pots etc.
Good Luck!
Longhair
Please, do read this thread. I know it is quite long. This slime algae is actually a bacteria, cyanobacteria. You are referring blue green algae. Totally different.