Pretty good flow, but not a lot compared to some of the systems I'm seeing people put togther. Probably around 25-30x turnover per hour in a 40 gallon tank. The green mille got even shaggier when I moved it to the top of the tank closer to the light and under more intense random flow from the sea swirl and wavemakers. However, the the green came out more with less polyp extension, the polyps kinda hid the coloration...