How to remove a vdev device from a Solaris 10 ZFS pool

I added a disk to a Solaris 10 server and was trying to add the device to an existing single disk pool as a mirrored device however, instead of using the "zpool attach tank c1t5d0" command, I used "zpool add tank c1t5d0"

zpool status gives me the following output

pool tank -state ONLINE -config

    NAME          STATE     READ WRITE CKSUM    tank         ONLINE       0     0     0        c1t4d0   ONLINE       0     0     0        c1t5d0   ONLINE       0     0     0

errors: No known data errors

When I try to remove the device using zpool remove or detach or offline, I get the following errors.

#zpool offline tank c1t5d0: Cannot offline c1t5d0: no valid replicas#zpool remove tank c1t5d0: Cannot remove c1t5d0: only inactive hot spares, cache, top-level, or log devices can be removed.#zpool detach tank c1t5d0: Cannot detach c1t5d0: only applicable to mirror or replacing vdevs.

I tried # zpool add tank mirror c1t4d0 c1t5d0, but I get:invalid vdev specificationUse '-f' to override the following error:/dev/dsk/c1t4d0s0 is part of active ZFS pool tank. Please see zpool(1M).

When I use '-f' I get the following error:invalid vdev specificationThe following errors must be manually repaired:/dev/dsk/c1t4d0s0 is part of active ZFS pool tank. Please see zpool(1M).

I get the same errors with # zpool attach.

Any help would be greatly appreciated.