I think the short answer is as much as you can. I think anywhere from 98 - 130lbs. This is 1.5-2lbs per gallon which seems to be a rule of thumb. I used 1.5lbs/gallon and have had a great deal of success. All my initial livestock is living and the water parameters are very stable.
You don't need anywhere near that much live rock to have a succesful system. I have a 92 gallon with about 70lbs along with a DSB and it's doing great after about a year and a half.
Put about 50lbs in and see if you like how it looks. If you want more, then add more. Keep in mind that live rock displaces water. If you put too much in you'll end up with a 65 gallon tank with about 30 gallons of actual water volume. At that point why would you need all that extra live rock? See my point? Go slow and get the look that you want, the DSB negates the need for exessive amounts of rock. It's up to you though.
Hasta
Jim
thanks for the reply guys. i think i am going to start with about 60 pounds.. btw where did you guys get your rocks? any place with good rocks and fair price?
It also depends on the type of rock. Fiji is more dense than Marshall and so you need more. I have 90 lbs of fiji in a 75G tank and it seems like plenty considering I will need room still to add coral, which is the whole purpose.
Depends on where you buy it. Carribean that is sold in Fl is rock brought here and grown here. Check out www.tampabaysaltater.com or www.gulf-view.com. I have known many people that have tried both and have had very very good feedback. Gulf-View is the grower for GARF. As far as Fiji they have to ship it a great distance and you pay the price. Carribean is somewhat more dense because Fiji and Marshall is usually old dead coral which is lighter but more expensive. Then there's the part about what they do to the reefs and all. Everyone has their own feelings on that.