Well I've had fish in my new 75 for a little over a week. 5 Gold Fish for a buck for cycling purposes. The lady at the pet store says that a under gravel filter is a must for anything 30gal or larger. Her reasoning behind this is harmfull bacteria that will grow in the rocks. I will be using my rock vacuum regularly. Shouldn't that take care of anything bad living in the rocks? This is like another $150 investment and seems like more of a pain than anything. I have found some articles advising against UG filtration and I would rather not go this route if it is not totally necassary. I didn't have it in my 45 and that seemed to do just fine. I currently am running a Fluval 304 canister rated for a 70gal and a HOB rated for a 40gal.

Any thoughts on this?