Is it necessary to wear tzitzit at night?

According to halacha, there is no obligation.

However, there is significance in this according to Kabbalah, as written by Maran the Ari zt"l in the book Pri Etz Chaim (Sha'ar HaTzitzit - Chapter 1): "There is no tallit and tzitzit at night, because...,

but the tallit katan should be worn even in bed, because at night..., and this does not cease even at nighttime.

And only the tallit of an adult is the only one that is nullified.

Therefore, it is advisable to be careful not to remove the tallit katan at any time, even while sleeping, except when entering the bathhouse. This is why King David himself was seen naked in the bathhouse, as it pertains to the mitzvot, and not while he was sleeping, for then he would have had a tallit katan."

Best of luck - Menashe Yisrael