if you havent started yet it is worth taking a look at http://www.glonation.com/ glow in the dark powders. not to sure about fish safe but maybe if you seal it up you will be alright.
They have the BEST glow powders out there for the price.
EDIT* Totally non-toxic these strontium based glow pigments come in a variety of amazing glow colors Right from glonation's website