Placement of Powerheads

[Lampshade]

try placing the powerheads widthways on the tank. With a coast to coast overflow you can disrupt a lot of flow having the powerheads pointing lengthways. For every bit of water the powerheads put out they need to take in the back side, so you are creating 2 opposing flows if everything is trying to flow in one direction. I noticed a lot better flow in my tank by moving the powerheads around a bit.

Lots of poeple like to create a barrell effect to pick up debris, I have my powerheads a bit more randomized, but for lots of people pointing powerheads widthways across the top of the tank will flow down the front glass and up the rockwork in the back of the tank(if that's how yours is placed).