Will a little food coloring in the water harm a goldfish?

I have to give a little science demonstration to some kids and their parents. I want to simulate a very simplistic river environment in a big jar. I thought it would be cool to have a small goldfish or two in the water. The science demonstration would work best if the water is slightly colored. If I add a few drops of food coloring to the water, will it harm (kill?) the fish?

FWIW, as a kid I remember seeing goldfish in small bowls of colored water as prizes at fairs. Given that 90% of them probably died of oxygen deprivation, I will not use that as a proof one way or the other.

Goldfish are pretty tough but fish are generally very sensitive to water chemistry. Don’t be surprised if he croaks. Actually, don’t be surprised if he croaks anyway if he’s being kept in a simple jar or fishbowl.

Would the goldfish change colors like a white rose would if placed in colored water? I think that the fishes gills might filter out the color and the color would soon fade away. And if the fish happens to die hey cheap humor

The University of California at Santa Barbara runs a website called ScienceLine, where the public can submit questions and receive answers from faculty. Stuyguy’s question was more or less asked here.

The answers seem to range from “probably won’t hurt anything” to “not sure”. One respondant suggested using colored lights as a safer alternative.

You could use Methylene Blue, it is standardly used as a anti-fungal agent for fish, get it at any pet store.
The fish in the jars you saw were most likely Betas that breath air and can live in some pretty yucky water.

Food coloring at a reasonable delution shouldn’t kill a goldfish. They are carp which is a mud rutting fish, that out live most fish in deoxigenated water. The heat or over feeding will be more likely to kill them. Maybe food coloring takes a couple days off their life of years. It’s not worth worrying about if it does.

You’re under 40, aren’t you? :smiley:

No, those were goldfish. They really did used to give away single feeder goldfish in those teeny glass bowls at fairs, back in the day. It was traditional for a kid to win one at the Ring Toss or Balloon Popping, transport it home in the car with great difficulty, keep it for a couple of days, and then have your dad dump it into the nearest body of water, as he explained to you kindly, “Honey, it’ll just die pretty soon anyway, it’ll be much happier out there in Lake Decatur with its other fishie friends.”

Which is where all those giant goldfish in Lake Decatur come from.

[goes back to rocking slowly on porch]


Hey hey now. I’m only 31 and remember this quite well. In fact, my nephew won a goldfish that way not more than…must have been seven or eight years ago. His mom wouldn’t let him keep him, so he wound up with us. And that sucker lived for another four years (R.I.P., Fishstick). And since that time, we’ve had two other goldfish that have lasted four-plus years. Dr. Fishopolous just died a couple of months ago, and Jaws, Jr. is still going quite strong.

All of them survived some pretty bad tank conditions at various times, and I can imagine Jaws, Jr. laughing and asking for more pain if we put food coloring in the tank. Think James Bond, Casino Royale, the chair scene. That’s our goldfish, man.


  1. You mean betta, not beta

  2. They can’t breathe air - although they’ll take gulps if there isn’t enough oxygen in the water

They used to sell a logwood additive to color your aquarium water.