As a general rule for flow you want to follow these guidelines. For FOWLR
(fish only) you want at least 10x tank volume in flow, so a 60 gallon would need at least 600 gallons per hour flow. For LPS
and softies you want at least 20x tank volume in flow, so for a 60 gallon you would want at least 1200 gallons per hour flow. For SPS
you want at least 30x so for a 60 gallon you would want at least 1800 gallons per hour. Keep in mind these are "MINIMUMS" but there can be to much flow or perhaps to direct of flow. You want water to flow everywhere in your tank but you don't want sand flying around and things getting blasted. Personally I have found that placing the powerheads on the back of the tank in each corner and facing them towards the front and slightly off the towards the center to work the best.