OK, so I picked up a K4 a couple of days ago to be used with my 150g tank that I am setting up. As some of you may know I have praised Seio's in the past, but I continue to be surprised with how well these Koralia's circulate water. Their flow pattern is so much wider than anything I've used in the past it's just unbelievable. I can't wait till the K5,6,7 &8's come out, they will be awesome.