Extend a system pool by volume

What is the trick to extending a system pool by volume?  I added four LUNs to the Celerra storage group and created two striped volumes on the Celerra. Now I need to add those volumes to my system pool. The Celerra will not automatically expand the pool and I can not get those volumes into it. Did I do something wrong? Maybe I should not have created the volumes before-hand. Any help would be appreciated.  Thanks.