You may not need a powerhead but is good to have on hand in case your return pump fails you will need flow in your tank until you get return pump going again.Let the coral be the judge. If things are closed up its likely to much flow(or light). If things are buldging open maybe turn it up just a bit like 5-10%. I often upgrade the return pumps in my aio's and don't even need a powerhead. But there always nice especially if you randomize/pulse the flow. And the return pump does count for turnover 30x is perfectly exceptable. And if you get a bit of simple sps put it in direct flow.