in need of a pump, any help?

[Shanspau]

I am looking for a pump to pull water from my aquarium to a filtration unit and back into the tank. Last night I purchased a powerhead rated at 295 gph at the suggestion of my LFS. Problem is, it's not moving 295 GPH, its more like 20-30gph. I need an external pump that will give me the GPH I desire, I want 300+. Any ideas?

 

[reef dummy]

What size tank? How high? etc. etc..

 

[Eric]

Iwaki

 

[Shanspau]

It's a new 40 gallon and it's about 2 foot from tank to filter and 2 foot back.