If put your goldfish in a tank with smaller and its tail turns red is lacy it just floats around what wrong it?

Stress: Sudden changes in the environment, such as introducing new tankmates or moving to a new tank, can stress goldfish. This can lead to changes in behavior and coloration. To reduce stress, provide the goldfish with a calm and stable environment, ensure sufficient space and hiding places, and gradually introduce any new changes.

Fin nipping: If the smaller tankmates are fin nippers, they may be attacking the goldfish's tail, causing it to turn red and become tattered. To prevent fin nipping, remove aggressive tankmates or separate them from the goldfish using a tank divider.

Disease or infection: Red, lacy fins can also be a symptom of a disease or infection. Check for other symptoms, such as white spots, cloudy eyes, or skin ulcers. If you suspect a disease, isolate the goldfish in a quarantine tank and treat the condition according to the veterinarian's instructions.

Water quality issues: Poor water quality can cause stress and make goldfish more susceptible to diseases and infections. Ensure the tank has a good filtration system and perform regular water changes to maintain proper water parameters (such as temperature, pH, and ammonia levels) suitable for goldfish.

Injury: The goldfish may have injured its tail on a sharp object in the tank. Inspect the tank for sharp edges or decorations that could cause injury and remove or modify them if necessary.

If you are unable to identify the cause of the goldfish's issues, it is recommended to consult with a veterinarian specializing in aquatic animals for proper diagnosis and treatment.