it is both hob and in sump it is curently in sump on my tank the pump im not curtian on but its been working fine for me i orginally had it on my 75 but then but it on my 125
this is a crappy picture from awhile ago but my camera is dead.you can set it like this where the pump is in the tank or you can put the hole thing in the sump i just did it this way because it is easier to access on the 125 because of the 3 doors but on a 90 it will be easy no matter how you do it
bit much for me
just to let you know i found them on the net for 220 with oceanrunner pump
but i know nothing about the the pump it might be worth it i dont know how well the skimmers hold their value