Whats under your rocks?
 

What is generally done with large tanks? Is it safe to put a couple hundred pounds of rock directly on the glass? What factors need to be considered ie. thickness of glass, type of stand etc.

I was going to use pvc discs but when I transfered everything over I forgot to use them.

Planning on adding grates or PVC, when I finally get things moved over.

What's the thickness of the glass on the bottom of your tank?

If it helps assuage you any, I plan on having at least 200lbs of rock on the glass of my 280 (3/4" bottom - you can practically park a car on it).

I've got about 90lbs of rock sitting on the glass in my 90. It never even occurred to me to put something under there but then the tank is barebottom and that would look kind of weird, IMO.

I honestly am scared at what I'd find under my rocks. LOL!

But my rocks are pushed down into the sand until they make as much glass contact as possible. (or sand poured around on initial set up) I try only to have limited rock touching the bottom for pedistals or supports and the majority of the rock making tables and shelves as clear above the bottom as possible. (ie 6 of 20 rocks touch the sand)

pieces of acrylic tubing...

My rocks are right on the glass. Under water they don't weigh that much.

agreed. I also have my tank on top of 3/4" styrofoam, then on a sheet of 3/4" plywood.

I have mine on reef-rack too in some parts to fill out the rock

I have my rock sitting on eggcrate and then I have a thin layer of sand covering the eggcrate. I have a little over 100lbs of LR in my 75G and I'll bet there's not more than 6 to 8 square inches of rock touching the sand.