Many of use magnets in our aquariums, some equipment comes with them and sometimes we make our own shelves and racks. Someone here gave me the idea of making a shelf out of rock to isolate some aggressive species on the back wall.






I get my magnets from K&J magnetics, and I get their monthly newsletter and coupon. This month, they did a blog on using magnets in aquariums. It has some pretty good info for people considering making their own magnetic projects.

http://www.kjmagnetics.com/blog.asp?p=aquarium

The blog includes a chart letting you know which magnet to pick based on glass thickness and how much weight you want it to hold.

"...a pair of small D84PC-BLK magnets on either side of a 1/8” thick glass wall should hold with a force of about 1.39 lb. This means it takes 1.39 lb to pull one magnet away from the wall. How much force will it take to slide the magnet down the wall? If we estimate half that value, that would be about 0.7 lb."

I didn't know how much the rock would weigh when I ordered the magnets, so I just stacked a bunch of them until it held.