We use multiple currency. When vendor invoice us in foreign currency, we use QB rates. I realise that when payment is done QB calculates its own exchange gain or loss. how do i reverse this or cancel it.(where is the transaction?) 

Note : I pass the difference in exchange manually when payment is done.Also change the rate  according to payment conversion (this is done when buying in another currency to pay particular foreign currency) ie. Buy EURO in USD (using USD Bank Account), to pay EURO - these are foreign currency . Home currency is SGD.

Is there any other effective way to post the transaction.