I decided I didn't have enough random current in my 300 gallon reef tank. I had 5 power heads on timers, that averaged from 300gph to 1000gph. This was okay for years but not great. Too many wires for one thing. I bought 2 of the model #8 koralia pumps (fan) that put out 3000gph. One at each end with a timer that turns one on and the other off at 1 minute intervals. After almost blowing the rocks in my reef over, I finally got them positioned to cause a significant current that flows both ways.
My point is that these things really blow (in a good way). Now I will monitor the corals and see if any of them don't like the extra current.