Two questions - Fish? Sand Vs gravel

In my reading and searching through the threads here, I notice there are a lot of factors in sand vs gravel. Most come into play with saltwater if I am understanding correcly. Having only freshwater would it be okay to use sand? What kind of sand? Could I go down to Lake Erie grab a few buckets of sand/gravel/rocks wash it as suggested in another thread (hose till it runs clear, add conditioner, add to tank) - or will I never get the bad stuff out?

I was thinking that a mixed size (gravel and sand) would be best to keep the look I want and the best for plants.

Second, I've stopped going to petsmart and started visiting a local small fish shop. He said he has on order "mini freshwater stingrays". They look exactly the same but don't get big. I cannot find these anywhere on the net. Are these just babies that will grow too large for a 30gal tank or is there such a thing?

wataugachicken: I read the same thing about the rays. But this guy said he ordered about 40 of them and the go quicly. I'll try to get the genus and species from him today.

I had the same fears you mentioned about the sand from Lake Erie but had to ask because it's the theme I'm looking to do. I will simply look for sand and gravel that can closly mimic the natural bottom of Lake Erie. On that what about rocks? Slate and such? Do you think that is safe enough?

Kasakato: Thanks for the tips, I guess I have some running around to do. Not that slate is very expensive but there are many streams and I have access to some shale beaches around lake erie. I know the significant difference between shale and slate but would that pose an issue if I just grab something from "the wild"?