Not really, no. You can only actively participate in one Sharetank at a time but you are able to leave and join another Sharetank if invited without deleting your current Sharetank balance.
Please note:
If you join another Sharetank, all members of your existing Sharetank will lose access if you are the owner.
To regain access of your old Sharetank balance, just leave the new Sharetank you joined.