If it's still in Pellet form, you should keep in the fridge.
If it's already converted, no need to keep in fridge. Just keep it away from light.
If your planning to convert the pellets and the pellets have been in the fridge, take the pellets out about 24 hours before you convert and have them sit at room temperture. If you try to convert the pellets immedietly from the fridge, it will take alot longer for the pellets to disolve.