Just be warned... I employed 2 emeralds in my 45 for the same reason: bubble algae! It was incredible how quickly these emeralds got the bubble algae under control! In fact, within a couple months, the tank was COMPLETELY RID of the algae. (Grant it, I did suck a couple out when I could get them without popping them, with the turkey baster; but most credit goes to the emeralds...)
However, the emeralds became quite active -- even during the day. They would wave the pinchers whenever the fish were being fed, or even swimming closely to them... One morning I awoke to a 1 finned toby puffer... Blasted emerald grabbed the fin right off the fish... (Perhaps because it was a slower fish...?)
Fortunately, the fish was healthy and able to recover; the emeralds found their new home at the LFS...
All said, they are GREAT bubble algae eaters!