Ultraviolet light is beneficial to aquarium goldfish. The UV acts as a water sterilizer, killing bacteria and algae.
and light Gold fish black
Jack Dempsey has over 20 years of experience with freshwater aquariums, his goal is to help beginners avoid the biggest mistakes when getting started. Do Goldfish Sleep? TBH the blacklight didn't make them glo very much at all. In hot climates, it is important that pond temperatures do not rise to dangerously high levels which will kill the fish.
How Much Light?
In fact, without exposure to UV light, the goldfish pigments would be under-stimulated. Full spectrum light is the important thing to note here. Add ammonia reduction chemicals to the tank, or for an emergency release of ammonia, change the water 25 percent daily for one week until the symptoms die down.