Moved my 125gal from the basement to the main floor by myself. Now THAT was a bugger. Not cuz it was so heavy, just annoyingly awkeward. Especially going up the stairs and all.
The only fish i know of that has broken a glass tank that i can voch for was a 2' snakehead in a old 75 gowing for a goldfish in the corner i was not there but i seen a cracked tank the next day. I don't belive cichlids have enough power to bust glass i would just not worry about that the only exception would be if u are lucky enough to own a 2'+ dovii,umbee,emperor, and then put them in a sinfully small tank that would have thiner glass but u are talking 300 gal or better so don't sweat it.
i always wondered about wether i should buy a huge acrylic glass for the above ground indoor pond...or should i get glass....as i was thinking acrylic but its too pricey...and i thought of just plain thick glass....but what happens when my sister and other lil siblings run into a 4' high glass with tons of waters and fishes with teeth....? im just afraid of what may happen if the lil kids are in the fish room and may knock over a tank and destroy it....=[....but on the other hand....go with glass its much clearer and stays scratch resistent...=]
i think those are concearns everyone has,part of the hobby, as far as seals letting go, if silicon is left out to open air, heat or even sunlight without water it will dry out over time and need to be cut out and re skinnned