Ah, mixing rhodamine WT. It comes in a 20% solution - we have 20 gallons of that. It's detectable at under 1 ppb - that's roughly 1.5 ml in an olympic swimming pool.
So I now have two gallon jugs; one has Rhodamine at 150,000 ppb, one at 800,000. My fingers are pink, my pants are pink. It's quite a pain.