My Hash is (a whopping) 6.63 GH/s however on the my account in Slush it is only: Total average hash rate in last 60 minutes: 4.309 Ghash/s

Is this normal?  It's been like this for weeks, but I just bothered to check.  I have two antminers and a bunch of old Block erupters.  They are connected to a Raspberry pi with three hubs.  Would I need to separate them out as different miners to get them to work? They worked at "full power" until I added a second antminer.

Thanks!