If you believe that BTS will come back, simply increase your collateral ratio as the price of BTS falls. There's no reason to allow a margin call. It's the same as selling low, and that's a bad strategy. Decide on your strategy first. You either believe in BTS long term or you don't. You could consider borrowing another HERO if the price drops down again. This would allow you to sell a second HERO at an even higher value. Then place a buy order for that second hero at the same value as your first trade.