Both skimmers are the same. The main difference between the CLSC-100HOB and the BH-100 is that the CLSC uses the new Aquatrance pump instead of the OTP pump.
Some vendors have not updated the name so they are selling the new CLSC-100HOB under the BH-100 name. We are working with all vendors to make sure they update the names so it does not create any confusion. We are no longer shipping BH-100 (OTP pump) skimmers. We are only shipping out CLSC-100HOB (Aquatrance pump) skimmers.
Note that the CLSC-100HOB has the skimmer inside the tank. The body is outside the tank but the pump itself is placed inside the tank. If you are looking for an HOB skimmer that has both the body and the pump outside the tank, then look at the CLSC-1000HOB. Also rated for 100 gallons. Just a different option.
http://www.coralvue.com/classic-1000hob-protein-skimmer
Hope this helps...