Merge container disks
I think disk is both partitioned and has container inside partition Container disk2, which is in use. And second partition Container disk 3, which was created probably by accident:



So press Partition button when hard disk is selected (ST1000LM..) and choose Partition. Then select unused partition and click [-] (minus) sign. 

Then select the main partition and increase its size to max:



Click apply and you are done.