diluted potions are less effective+undiluted more

idea from Spork
https://github.com/Bulwersator/CopyOfSporkHack/commit/a37cbf87d023fec33af23597e57f6657ff8744a4
refactor
erode also potions (=dilute)

previous commit in this topic: 2fc90b26bd929870c188dfb306254ed3bc8a5126