When you deposit HKD fiat to BtcEX Hong Kong bank account, it's always exchanged to USD balance & update to your BtcEX wallet.
Deposit & Withdrawal exchange rate is fixed in USD/HKD 7.75.
Example 1: Peter deposited 10,000 HKD to BtcEX Hong Kong bank account press deposit request, it's will update as USD balance in (10,000 / 7.75) to $1290.32 USD.
Example 2: Mary sold USDT to $2,000 USD balance in wallet process withdrawal $2,000 USD, BtcEX will deduct $100 HKD withdrawal fee deposit (2,000 * 7.75) - 100 = $15,400 HKD.