Well here starts the trouble with the whole "Freiwirtschaft" movement, surely our economy is heading for negative interest. But for an alternative currency grow

Well here starts the trouble with the whole "Freiwirtschaft" movement, surely our economy is heading for negative interest. But for an alternative currency growing within that economy, a negative interest rate may not be balanced at all. So maybe there is no fixed demurrage rate at 5% but instead this rate is just another price and should be adjusted accordingly to the state of the market (and may be positive or negative).