If mixing with eco complete, the sand will mostly settle on the bottom. I do think the eco complete has a slightly better CEC, but not by a whole lot. Probably only worth it for aesthetic reasons.
For the sand, each batch and vendor is a little different. I've had a fairly oily bag and one that was really clean. I'd personally rinse it first, but I do know some have just dumped it right in.
Sent from my Nexus 6 using Tapatalk