It;s not light alone, as i have seen a 120 with pc lighitng and long lashed zoas at the bottom, and i have some long lashed up high under 400w. I tend to think it is the flow, not nec. high flow, but random, oscillating flow. He had tunze stream in his tank, and so do, and we both have lashes. I have had some develop long lashes, and they were in a high flow area. All of my zoas that have longer lashes have been in captivity for at least a year, some much longer. The longest lashed zos have been in a tank for over 3 years.