You can get a cheap fan that clips to the side of the tank for 10 bucks at wal****. If you are careful you MIGHT be able to get away with it. I lost an entire colony though to Bacterial infections because of the heat. I added a fan, and the shrimp survived.
Blue pearl in 78 is more than okay, I actually prefer this temp for Neocaridina as they grow faster and breed better. Don't over feed to avoid bacteria infection. If possible, add an air stone or increase surface agitation to increase oxygen level.