Or you can put a 1.5" pvc spacer pipe in between both buckets.I suggest raising the buckets 1-2" above the controll bucket, it is not personal preference but a flaw with the cap system if all buckets are level with control bucket you will notice water sitting in the bottom of the buckets after drain cycle. This causes problems in later flower/veg when roots hit the bottom of the lower bucket, the sitting water stagnates quick in the site due to black buckets sitting under high intensity lights. The roots sit in stagnate water causes sick plants and root rot.