Unbreakable

Hello. I have a disk pool of 4x10TB drives that were getting full. So i added two additional 10TB drives. I noticed that the old drives data remained where it was even after running a "rebalance" each drive near 90% while the new drives are almost empty. I would like to have approximately the same amount of free space across the drives which i am not seeing. I poked around the options with the different balancers and I am not seeing any setting for this unless I am just not undertanding. Up on the Stable Bit website there is a link to a balancer called "Disk Space Equalizer" but when I try to install it iI I get the error "StableBit DrivePool 2.X needs to be installed before installing this plug-in." I am currently running version 2.2.5.1237 so i am not sure why its not installing. BTW, I am not using ANY duplication if that matters. Any thoughts on what I can try?