whats the difference between marcos rocks and big rocks i have outside?

[BiggySmalls]

if i was to put the big rocks i have outside in my tank after cleaning and washing them
would there be any difference since marco rock is dead and dry already?

[ggk1988]

Depends on where you live, but more than likely the rocks have different compositions.

[Caragol]

Generally they might not be as porous and might have undesirable mineral content. Is this for fish only or for reef?

[R.W.]

marco rocks are dried up reef rocks i believe and the rocks you have outside are earthy and contain many silicates which is a bad thing in a reef. There may also be other minerals in the rocks from outside that you had no idea they were even there.

[BiggySmalls]

ok thanks

[HammerDude33]

if you spend a little time researching the procedure, you can create your own rock out of concrete very easily and affordably.

here:
http://saltaquarium.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=saltaquarium&zu=http%3A%2F%2Fwww.geocities.com%2FCapeCanaveral%2FHangar%2F6279%2FRaiseCementRock.html