Agreed. Too big is better than too small. The eaiest thing that i have found is to simply aim the powerheads into one another or at the glass. It allows you to use larger powerheads, the resulting flow is very chaotic, and your animals dont get hit directly.
this is what im doing and have been trying to do
yes by aiming two powerheads toward themselves you can make pulsing waves to deaden the power of flow