The flow rate is usually 20 to 30 times your volume of your tank but can depend on what type of corals you choose to have if you're going for more of a SPS then I would go for the 30 times and if not could go to 20 times but these are just rough guidelines some people go higher some people go lower also has a lot to do with all the way your rocks laid out where most of of us try to aim to have no dead spots.