You could let the balance fall below $30 in your example because it’s a loan (“borrow”), not a deposit. If you’re claiming to hold the funds on their behalf an

You could let the balance fall below $30 in your example because it’s a loan (“borrow”), not a deposit. If you’re claiming to hold the funds on their behalf and do otherwise (like “investing” them in your less than arm’s length hedge fund), then you’re breaking your fiduciary obligations.