Don't get me wrong, I still use slate for my Balloon Green Terrors tank, but when I was younger I had a beautiful 55 gallon setup that was months and months in the making. I had lots of slate in there. My first and only fish I put in there was an Oscar. A couple of months later my oscar started ramming stuff, and knock a piece of slte loose...and of course the slate slid down and cracked the glass. 15 years and multiple tanks later I think I may be a bit wiser. And thank goodness for silicone.