River sand vs. Concrete sand?

[pineychickenlady]

I have both in my pens
The concrete sand you mention is mason sand and is actually better for keeping clean just make real sure it doesnt have any polimers or silicon in it because its poisunous to your birds
River sand can also have bad things in it so whatever you decide
have it checked out for microbials before putting it in your pens

How do you have sand checked for microbials?