ZHU CTLR EXPERIENCED OPERROR AT FL300 DURING SEQUENCING ATTEMPTS; FAILING TO RECOGNIZE LOSS OF SEPARATION WITH PRECEDING TFC.

Narrative

I WAS WORKING A HIGH AND LOW ALT SECTOR COMBINED. WHEN RELIEVING THE PREVIOUS CTLR I WAS ADVISED THAT WE WERE METERING (CTAS). THIS WAS THE FIRST TIME I HAD UTILIZED CTAS IN APPROX 6 MONTHS. AFTER TAKING OVER THE SECTOR; THE RADAR ASSOCIATE (D SIDE) AND I BEGAN TO DISCUSS THE METERING LIST AND THE CORRECT DATA ENTRIES FOR MANIPULATING THE ACFT IN THE CTAS LIST. THERE WERE APPROX 3 ACFT WITH REQUIRED DELAYS OF 3 OR 4 MINS IN THE CTAS LIST. IN ORDER TO MEET THE CTAS DELAY TIMES; I ASKED ACR Y (E170) TO REDUCE SPD AS MUCH AS PRACTICAL. I DETERMINED THAT THIS WAS NOT GOING TO BE SUFFICIENT TO MEET THE DELAY TIMES ON THIS ACFT AND DETERMINED THAT AN OFF COURSE VECTOR WOULD BE REQUIRED. AT THIS TIME I WAS AWARE THAT THIS ACFT HAD PARALLEL TFC AT THE SAME ALT AND WOULD HAVE TO BE DSNDED AS HE WAS BEING VECTORED. I TOLD THIS ACFT TO TURN 30 DEGS TO THE R AND DSND AND MAINTAIN FL300. WHILE TRYING TO SET UP THE SEQUENCE AND PROVIDE SEPARATION FROM THE TFC AT FL320; I FORGOT ABOUT THE ACFT AT FL300 THAT WAS LESS THAN 5 MI IN FRONT OF THE E170 I WAS DSNDING TO FL300. I NOTICED THE ADDITIONAL TFC WHEN THE E170 WAS LEAVING FL318 AND TOLD HIM TO MAINTAIN FL310. HE REPLIED THAT HE WOULD MAINTAIN FL310 BUT HE WOULD PROBABLY GO THROUGH IT. THE E170 DSNDED TO FL303 BEFORE RETURNING TO FL310 AND SEPARATION WAS LOST. THE SECTORS THAT I WAS WORKING ARE NOT SEQUENCING SECTORS AND THEREFORE ARE NOT SET UP FOR VECTORING ACFT FOR IN-TRAIL. CTAS IS SO INFREQUENTLY USED AS TO BE VERY CUMBERSOME WHEN IT IS. IT REQUIRED A SIGNIFICANT AMOUNT OF OUR TIME AND THOUGHT PROCESSES AND IN MY OPINION WAS A MAJOR CONTRIBUTING FACTOR IN THIS LOSS OF SEPARATION. THE E145 THAT WAS INVOLVED IN THE LOSS OF SEPARATION WAS VACATING MY AIRSPACE AND I HAD TURNED MY ATTN TO THE 2 ACFT THAT I HAD VECTORED AT EACH OTHER AT THE SAME ALT.