I have two 25's on a 50 gallon pentagon. Raven has provided the correct info for the control box and I second his recommendation to leave room for the control and power cords coming from the bottom of the control box. I'm very pleased with these pumps. I have one mounted at the top and another mounted vertically on the opposite side. They replaced a couple of MP-10 which are in my opinion not worth the money. All three of my wetsides have suffered from ceramic shaft cracking within 3 months of operation.
In my case , the RW's are dead quiet but I'm running them on low. They can produce a lot of flow and they are easy to clean. I have each side of the individual pumps operating in different directions.