There were a few I really liked: PJ (short for Purple Jelly), Ms. Yukari, Jr., Twitchy, and Library Monster were contenders. But, in the end, I chose Mr. Westing as the betta's name. It was suggested by Ethan in 5th grade who recently read and enjoyed The Westing Game by Ellen Raskin (FIC RAS).
It's a book that I also highly recommend. It is a fantastic, very sophisticated mystery that won the 1979 Newbery Medal. It was my best friend’s favorite book growing up and she recommended it to me as an adult. If I remember correctly, I read it in my late-20s and I was riveted by the plot.
I hope Mr. Westing is comfortable in his bigger tank and enjoys hearing the library read alouds as much as the kids do!