You can’t add drives to the pool like that.  When you added the 4 drives, it created an internal RAID group in a 2+2 configuration.  If you add four more drives to the pool, it will create another RAID group to serve the pool, in a 2+2 configuration.  Your only solution is to get your pool properly balanced recreate the pool from scratch.  Basically, backup your data and restore it.  Or, given enough spare drives, create a second pool and migrate luns to that pool – non disruptive, but it will require more drives.
Hi,  Recently, as a matter of urgency to handle the capacity pressure we have added 4 disks in to a Pool with in capacity tier (Raid 6 (6+2)). This has added disks to the Pool and created a RG with 2 + 2 disks with RAID 6.  I would like to understand the steps involved to add the remaining 4 disks to the raid group within the pool and rebalance the data within the raid group or pool.  Regards, Krishna
How to add disks to an existing pool RaidGroup?