I sold my freshwater soul...

[J. H.]

is it possible to stack rocks without the use of the egg crate or styrofoam? In freshwater, without the tank cracking?

Yes, but with added weight, you get closer and closer to what the glass can take from the contact points you are offering. The eggcrate/styrofoam offers the ability to spread the weight and multiply the max load incredibly. The glass on the bottom of your tanks is very strong, but do you want to find out exactly how strong?

 

[twentyleagues]

you can get a sheet of egg crate at lowes or homedepot for around $10.