You are taking a loss, but you could try to use it as a way to fake a lower costbasis. Sort of. Maybe. Before, you didn't have any costbasis (well you did, for the electricity, but its going to be hard to report that). If you bought some at $800, you could try and claim it as a "reasonable" cost basis. Its a pretty dumb idea, though, as youre no less likely to be caught as if you just didn't report your Bitcoin gains for taxes at all.