How much rock(weight) is too much?

If you put a one cubic foot, 100 pound rock in an aquarium, filled with water, the rock only pushes down on the bottom of the tank a bit less than 38 pounds. Water buoys up anything put in it by an amount equal to the weight of the displaced water. I think that is what saves our tanks from ruptured bottoms. I suspect there is a limit to how much rock you can use, and I know you shouldn't let pointed protrusions on the rock press against the glass. Some people use a plastic pad under the substrate when using heavy rocks, to protect the glass.

 

I would protect the bottom of the tank. Styrofoam, especially the dense stuff, is nice to use as padding for rocks. A couple dabs of silicon will hold the Styrofoam nicely.

I never have seen, or even recall hearing of a case of a rock breaking aquarium glass for any cause other than mishandling or unstable placement.

But still, that is a big rock for a 37 gallon tank!

Biollante