Thank you all for your advice! I appreciate it
I think today I will pick up a dark background for the tank and new substrate. Do you think I could mix the neon substrate with the black and still get a good effect? My daughter really wants the bright colors in there somewhere.
I was also thinking about what I could do about the light source. It currently has incandescent lighting, which I'm not a fan of. I think flourecent would be a better choice. I read somewhere that lighting with a blue tinge is probably the best.
I suggested guppies to my daughter, but she didn't really like the look of them. She's really attracted to the glowy fish. My friend has a ton of guppies that she's been trying to pawn on people who want them. She had a bit of a population explosion.