I'd like to open a trading account with thinkorswim and understand that they are looking for a min. opening balance of $3500. Does that mean that my account should be valued at 3500 minimum? In other words, what happens if I buy 3500 worth of stock, but it drops the following day and my value is now 3000? Will I need to add $500 to my account? Conversely, if 3500 is needed to open an account, but there are no minimum value requirements, can I deposit 3500 but then withdraw 3000 and trade with $500 only? thanks in advance.