Since he just bought the Nautilus Mini and had only used it for a few minutes I can almost guarantee he had the 1.6ohm coil that comes preinstalled in it. The only other alternative is the 1.8ohm coil, but both should work at similar wattages.
I've run both the 1.6ohm and 1.8ohm coils at 19W with a clear 50/50 mix. I've run them both at 15W with a gold colored 60/40 mix. They both work nearly identically at those wattages.