Well, I thought that 36% was still too much ethanol. I was right. On the way to work this morning, I got another CEL. I got off and added another 3.592 gallons of Amoco Ultimate to the tank.
So... tank #4 statistics:
Gallons from tank 3: 12.8
Ethanol content of tank 3: 36.435%
Gallons of 93 Octane Amoco Ultimate: 3.592
Ethanol content of tank 4: 30.6273%
Octane of tank 4: 94.31
I'll clear the code after work tonight and see what happens.