The temp range for fermenting is usually posted on the container.
If your daytime temp is 72 that's a good temp for weizens. If your nighttime temp drops to 62 then, while it's not optimum, your yeast just slows down a bit. Ale yeasts just go a little dormant at the lower temps. That's all.
I don't think you have anything to worry about your brew, but place a sweatshirt on it at night. This'll help the fermenter maintain a steady temp.
You do not need to add more yeast, just try to maintain a good temp.