i agree with veriann. i have made my own rocks. we made 250 lbs for our last tank. the concept is a good one. i never thought they were porous enough and they weighed a lot.
the time waiting for them to cure is a bummer too. but if you want to give it a try then garf is a great place to look. look at their howto movies as well and there is a short video of making aragocrete arches to give you an idea of how they do it.
