I have one in my 75 sps tank and really need a second one but it all depends on you rock work . If you dont have to much rock high up then on is good . I have 125lbs of live rock so flow is hard to get in the other end of the tank.
I have 1 on my 75 as well as well as a sea swirl and korilla on the back walls I wish I had a mp 20 for the other end I see deritius build up on the rocks because of not enough flow
I have one in my 156 and I keep it on reef crest. I also pegged my rocks up off the sand bed about 1.5 to 2 inches so my flow is more constant and the other thing I did to increase my flow was I put two 5500 maxi jet pumps for my returns one on each. It's all how you set it up.