How is Zakat on money calculated, and what are its legitimate recipients? What is the ruling on one who issued a fatwa that the Zakat threshold (nisab) is 1800 Egyptian pounds based on silver, not gold, due to the high price of gold?

Zakat is obligatory on banknotes if their value reaches the nisab of gold (85 grams) or silver (595 grams), and a full year (hawl) has passed on them. For example, if a person has 1800 Egyptian Pounds that equal the nisab of silver, and a full year has passed on them, then Zakat becomes obligatory upon him.