How did my fish get ick and what can I do to treat it?

Ich, or white spot disease, is a common parasitic infection in fish caused by the protozoan Ichthyophthirius multifiliis. Fish can get ich from poor water quality, stress, or introduction of infected fish. To treat ich, you can raise the water temperature to 86F for a few days, use aquarium salt, or medicate with anti-parasitic medications. It's important to also improve water quality and reduce stress for your fish.