Check Constantly on Data in Table

Hi All,
        I have a table named tblAccounts in my database and in that a column named "Amount" of type decimal.This field keeps on updating on every transaction(+ or -) . Now i need 2 update the column Amount (some amount X = X + 1,00,000 )when it becomes less than some particular amount like 1,00,000 . how i can do this.

Thanks in Advance
Vishwas