how much flow for powerhead for a 20 gal cube?

[mfp4073]

Need some advice. I dont know such things which is why I ask the MOST KNOWLEDGABLE web board around (did that encourage your response?). I need a powerhead for my tank. Its the kind that has the overflow in the back with mini "refugium/heater/bioball" space. The powerhead is the one that moves the water from the back area to return it to the tank. How much flow/gph/rating should I be looking for?

THANKS!

 

[mfp4073]

bump

 

[HotRod68Camaro]

depends on the type of coral you want to keep.