As much as you can fit into the tank without throwing it in and preferrably
not V shaped, probably safer to have flat bottomed rocks for the mass to be
evernly distributed on the tank bottom. I think you missed a newsgroup in
your post.

"Eddie" wrote in message
...
Hi,

I'm thinking to put my river rock into my 3' feet tank for my cichlids.
How many KGs of rocks can my tank support?
Tank specs :
36 inch X 18 inch X 18inch
glass thickness : 5mm

Currently I have 30 KGs of rocks, will my tank break if I put all the
rocks
in?

Please let me know and Thanx...
Eddie