Squeal from Engine after replacing Water Pump and Serpentine Belt

[vidfan]

Hi, I have an 08 Yaris with 43,000 Miles.
A few weeks ago I had to replace the Water Pump and Serpentine Belt. I had noticed after being installed, I had a constant squealing noise. My father-in-law, who helped me with the install, said it was a bad pump. I drove the car home with on/off squealing and was about to get a new pump when I decided to try tightening the belt. I loosened the bolt on the tension arm, used a crowbar to pull the alternator out as far as possible, then tightened the bolt. The squealing had stopped!

A few days later it slowly started back up again. I thought maybe the belt had to be retightened due to being stretched on first used. But now it's slowly starting again.

Is there anything else I need to do? I bought the belt from Rock Auto, DAYCO Part # 465K4.