308 Mikvah for Men before Davening
The prevailing custom among chassidim is to immerse in a mikvah every day before davening (with the exception of Yom Kippur and Tish’ah B'av), and especially on Erev Shabbos and Shabbos, as well as Erev Yom Tov and Yom Tov. There are sources indicating that there were those who had a custom of going every third day, so as not to go three days without mikvah, and some who had the custom of going Monday, Thursday, Friday, and Shabbos.
There are a number of reasons for immersing every morning, among them: 1) One immerses as preparation for davening, since mikvah can achieve a high level of purity for davening. 2) When a person davens, he resembles a Kohen Gadol who immersed in the mikvah every day. 3) It is a symbolic of teshuvah, and facilitates teshuvah every single day. 4) Daily immersion prevents others from knowing whether a person is going to the mikvah because he needs to purify himself—as done by many who follow the stringency of Tevilas Ezra—or because he wishes to attain a higher level of purity. Although one should make every effort to go to the mikvah before Shacharis—as many of the reasons apply specifically to the morning—in case he didn’t have the chance to do so, it is nevertheless a good idea to go after davening as a symbol of teshuvah, and in preparation for davening minchah.