When did they see that there is much money in the Aron?
'Rashi', Rashi (Melachim II, 12:11): Every day (constantly). They would empty it out and return it to its place. Malbim ? this is unlike the Aron near the Mizbe'ach. Refer to Melachim II, 12:11:1:2.
Here it says that Sofer ha'Melech and the Kohen Gadol's appointee counted the money. In Melachim II, 12:11 it says that Sofer ha'Melech and the Kohen Gadol counted it!
'Rashi': Also there, it means that the Kohen Gadol sent his Shali'ach (the Segan) to count. It is not honorable for the Kohen Gadol to go with the king's servant.
What is the meaning of "vi'Aru Es ha'Aron"?
'Rashi', Radak: This is [pouring out, like] "va'Te'ar Kadah" (Bereishis 24:20).
