Fish owners know that decor is an important part of personalizing an aquarium. Castles, rocks and houses make a fish tank fun. Some fish need or prefer caves and other places to hide. However, aquarium decorations can chip and fade over time. Many people like to repaint aquarium decor to make it fresh and new, and some people even create and paint their own aquarium decor. Painting aquarium decorations takes some thought. Some paints can be harmful to fish, and some paints don't do well underwater.