How necessary are they? I only ask because I came back from my LFS and they have two of the most beautifully planted aquariums I've ever seen. Both are 75 gal (like mine) and they have two power heads in each. I'm currently using an Eheim canister filter and the output just breaks the surface. I thought this was enough for water movement but now I'm wondering. I also run a bubble wall along the back. Now I'm debating on what a power head would do for me as well.