DIY Rock formation

[bnt1]

I have a fresh water 55 gal. tank I just have a few fish nothing major 3 guppies, 2 plattys, 2 tetras and a sucker fish. I would like to create my own rock formation to sum-what look like a reef. Does anyone know what materials if any could be used safely and where could I find them near Chicago.

Thanks for any info.

 

[marshrunner]

Do a search for aragocrete. I made about 80# of it and is now in my 55gal reef tank. It takes about 6 weeks to cure, but is easy to make. My mixture was 1 part portland cement, 2 parts crushed oyster shell and 2 parts solar salt.