Fwiw,
This is the powerhead I selected to use in my IM 40. Many recommend around 25X the tank volume in flow, which would be 1,000 gph. This Tunze Nanostream can also be controlled by an Apex, which was a requirement for me.
I mentioned an MP 40 also, which would have to be turned down a good bit, but could also work.
www.bulkreefsupply.com
This is the powerhead I selected to use in my IM 40. Many recommend around 25X the tank volume in flow, which would be 1,000 gph. This Tunze Nanostream can also be controlled by an Apex, which was a requirement for me.
I mentioned an MP 40 also, which would have to be turned down a good bit, but could also work.

Turbelle Nanostream 6040 (53 - 1,190 GPH)
German-made Tunze powerheads are one of the best high flow powerheads available. They are smaller and can be hidden in the aquarium easier than competing brands. Tunze pumps can be configured in a wide range of positions to target any area of the tank. For aquariums from 5.3 - 132 gallons Flow...
