SanHQ provides a stat on replication "Reserve in Use Percent" which shows how much of your replica reserve space on the partner you are using for any given volume.
I want to grab that stat, or even the usage in GB from the eql powershell scripts but having a hard time finding where I can grab that.
Have you tried any of the GetReplica CMDLETs?
The PowerShell Reference guide has more info on these. http://eqlsupport.dell.com/
I don't work much with PowerShell but hopefully this will point you in the right direction.
Social Media and Community Professional#IWork4DellGet Support on Twitter - @dellcarespro