As far as the fit. on the website it gives eternal and internal dimensions my tank is a corner tank that the two biggest sides are 24 inches on the bigger fuge the internal dimension is 26 with the power head on. Question 2 ,yes this is the only skimmer I am using my tank is 48 gal before sand and lr. so it works for me. If it was a 75 i would run the bak pak2 also. (i would also have the bigger fuge) Oh I have a glass top also (custom cut) the gap on that side is 2 inches fits just fine for me. The glass doesnt hit the return pipe but just by a 1/4 inch. My next step for me is to upgrade lighting. Im gonna go mh so the glass top will probably get the boot, for cooling issues. Just noticed that your tank is a 72 if you have the space then imo i would run both, really up to you. About the mareland skimmer you have, I have never used one but people on here dont like the bak pak 2 either so we are in the same boat, welcome aboard. lol