my powerheads are marineland 301 and 201. i bellieve they are 170 and 95 gph repectively. i have the both aimed to the center so they beat each other up. its enough flow that i dont have any bad algaes, so im happy. ive got one dead spot behind the rock on the left that gets a little build up, but the crabs congregate there, and are easy pickens for the mantis.