Flagstone?

[Marx]

is it safe for aquarium use?

my dad has 5 huge peices i can take and break up to use in my tank? just wonering if its safe..

Thanks...

[manytanks]

As usual, test a piece of the flagstone rock with some hydrochloric acid (aka Muriatic acid) from your friendly neighbourhood hardware store or Canadian Tire's paint department. If it fizzes vigorously, it's generally not good for your tank.