This is 6 hrs after 1st harvest. Rubbish vid I know, but you must be used to my video ability by now. Rumpy Pumpy - filamentous algae only require light, nutrient (enhanced flow or otherwise), predation free substrate and opportunity to exist. This screen is a pre matured ex waterfall screen which has speeded things up a lot. Flow is different from the small version, but on that one it was the left and right flow that was being tested as it filled and emptied, not actually the water going up and down. This new flow seems to have improved things as it oscillates more like natural conditions. Light is supplied by 80 ish watts of cheap grow LEDs so there's also scope for improvement there. Another benefit is that when the screen is cleaned with fingertips, it tears the algae which leaves a good base of algae for the next growth period. Edit - Rumpy Pumpy, just looked at your thread again. There tends to be no benefit in having the screen more than 3 inches under the water. I don't know how deep your screen is but deeper means further away from the light. I'm gonna state again that your lights are very weak it seems to me. All those cable ties are probably reducing the light reaching the screen even more. Youll notice I have drastically reduced the amount of ties on mine to get the screen growing rather than the ties. I'm keeping my eyes on the few I have though to see if there really is a benefit, or not.