Is Zakat obligatory on the total surplus money from salaries in the bank account if some of it has not reached the hawl (one year) or the nisab (minimum threshold), while there is a large debt to the bank?

Zakat is not obligatory in Ramadan except on the nisab (minimum threshold) that has completed a full lunar year (hawl). If there is nisab that has completed a full lunar year, and other wealth that has not yet completed a full lunar year, Zakat is only obligatory on the former. It is permissible to pay Zakat in advance for wealth that has not yet completed a full lunar year. Debt prevents Zakat on intrinsic wealth. If there is no other wealth to cover the remaining installments, then Zakat is not obligatory.