Liquid Erchius is too easy to get. One trip to a moon can result in thousands of units of the stuff. Erchius Crystals make much more sense, as you have to do a mission to get some. One crystal should be refined from 5 units of liquid, and provide one fuel. This means that it now takes 5000 Liquid Erchius to completely fill your tank. After all, if you need a crystal to fix your ship, you should need a crystal to fuel it!
