Win 8.1 Storage Pool not allowing "add drive" nor allow expand capacity

Question

Have one Storage Space within one Storage Pool (Parity mode) containing 4 identical hard drives.
Used for data storage, it appears to be functioning normally
and
has filled 88% of capacity
(ie. 88% x 2/3 of physical capacity (parity mode))
The only other storage on this new PC is an SSD used for OS (win 8.1 pro) and application software.
In "Manage Storage Spaces"
displays this warning message to add drives:
<   Warning                               >
<   Low capacity; add 3 drives   >
After clicking "add drives", it displays:
"No drives that work with Storage Spaces are available. Make sure that the drives that you want to use are connected.".
However I had connected another two identical hard drives via SATA cables and "Disk Management" displays these two drives available.
in summary:
"Manage Storage Spaces" does not find these drives as available although they show correctly in Disk Management.
btw - I removed the pre-existing partitioning on the 'new' drives so now they show only as "unallocated" in "Disk Management". (I did
likewise before Storage Pool found the 4 original drives)
Perhaps the problem is to increase the total nominal capacity of the Storage Space, before can add more drives?
Microsoft says that the capacity of Storage Pools can be increased but cannot be decreased -
but computer displays no Change "button" by which this can be done. There is supposed to be a "Change" button but that is
not displaying for me. So "Manage Storage Spaces" offer me no option to manage the "size" of the pool.
only five options are displayed:
Create a storage space     (ie. from the small amount remaining unused in the Pool)
Add drives     (.... as explained already)
Rename pool    (only renames the storage space)
Format        (ie. re-format and so lose all current data)
Delete         (ie. delete the storage space and so lose all current data)
using Google, find nothing bearing on this problem
except the most basic instructions to set up a storage space!
Can you help?
The problem is that the Storage Pool is not displaying a "button" to increase capacity, and when click "add drives" finds no hard drives available. 

Answer 1

Hi,
I would suggest you launch Device Manager, then expand
Disk drives. Right-click the disk listed as "Disk drive", and select
Uninstall. On the Action menu, click Scan for hardware changes to reinstall the disk.
Please also take a look of this link:
see this part: How do I increase pool capacity?
http://social.technet.microsoft.com/wiki/contents/articles/11382.storage-spaces-frequently-asked-questions-faq.aspx#How_do_I_increase_pool_capacity 
According to the link, to extend a parity space, the pool would need the appropriate number of columns available to accommodate the layout of the disk.
Yolanda Zhu
TechNet Community Support