This is what I went with on my IM 50 Lagoon. Very happy with it. Shopped around and got it for $225.00 shippedReef Octopus Classic 90 Hang-on-Back Protein Skimmer
Unique skimmer design with cylindrical body which uses the siphon to feed water to the skimmer. This reduces the load on the pump while increasing the air intake. Rated for aquariums up to 100 gallons Powered by Aquatrance 1000 Pinwheel Pump Design reduces turbulence Capable of surface skimming...www.bulkreefsupply.com
I have this on my 90 and it works great