I want to make a fry pile in my tank but ran out of smaller rocks. I do have about 5 million landscape rocks. Just not sure if they will be ok to use. They are man made I believe. They are white and look like a cross between quartz and marble. They are very hard. I tried smashing one on the concrete and couldn't get it to even chip. I soaked them for several hours to see if they changed the water and they didn't. Do you think they would be ok? Sorry if this is a stupid question.