wff,
I sometimes buy minnows at Hook, Line and Sinker in Lake Orion and the minnows are kept in water that is very blue. I believe some type of chemical is used but have never asked. The minnows I buy from there last much longer than any that I have bought at bait shops near Lake St. Clair. I once kept a 2 gallon bucket of minnows for over a week without changing the water, feeding, or caring for them and none died. You might want to check into this.