Fast for tefillin that fell in the month of Nissan
Question
b. If I want to redeem the fast by giving tzedakah (charity), how much money must I give?
Answer
Shalom and blessings
When a person’s tefillin fall and they were without a cover, the custom is to fast.
In the month of Nissan, according to Ashkenazi custom one does not fast even an individual fast. According to Sephardi custom, an individual is permitted to fast.
Therefore, an Ashkenazi should postpone the fast until the month of Iyar, while a Sephardi may fast immediately.
The custom is to actually fast and not to redeem the fast with money; however, the directive of our teacher Rabbi Amram Fried shlita is that bnei Torah should, instead of fasting, observe a taanit dibur (a “fast of speech,” refraining from speaking and devoting the time to learning).
The redemption of a fast is done by giving the monetary value of the meals one would have eaten that day.
Source
Shulchan Aruch, Orach Chaim 429