function force_refund(address _to_refund) onlyOwner {
    uint256 eth_to_withdraw = SafeMath.div(SafeMath.mul(balances[_to_refund], 100), 99);
    balances[_to_refund] = 0;
    balances_bonus[_to_refund] = 0;
    fees = SafeMath.sub(fees, SafeMath.div(eth_to_withdraw, FEE));
    _to_refund.transfer(eth_to_withdraw);
  }