personal experience is telling me you will have dead spots with just 1 powerhead. i was wrong about the specs of the wp40. but my three powerheads recommendation still stands. yes, in terms of turnover ratio, one wp40 is enough, but that's considering the tank very narrow and long. 50inches in my opinion is nowhere narrow by any standard. if you check out Mr. Saltwater tank on Youtube, you would see the setup he has for his 300+gal
tank. 3 of his powerheads are more than sufficient to cover the tank if you look at the spec, but he used 6, i believe, to cover all angles. what i meant to say before is that you can probably get 2 wp40 but run it at the low-medium range, so that you're not blowing water off the tank. but you WILL need more than 1 to cover a tank that size.