What are you doing wrong if after clean your goldfish tank they seem to become ill and sit on the bottom not moving much?

1. Water temperature shock: Rapid changes in water temperature during the cleaning process can cause stress and illness in goldfish. Make sure to adjust the temperature of new water to match that of the existing water in the tank before adding it.

2. Chemical imbalances: Adding too much or too little water conditioner, salt, or other chemicals during the cleaning process can disrupt the water's chemistry and make it harmful to goldfish. Always follow the recommended dosages on product labels.

3. Chlorine/Chloramine: If tap water is used to fill the tank, ensure that it has been properly dechlorinated. Chlorine and chloramine, commonly found in tap water, can be harmful to goldfish.

4. Physical damage: Be cautious when cleaning the tank to avoid injuring the goldfish. Rough handling or bumping into objects can cause stress and physical injuries.

5. Sudden pH changes: Rapid fluctuations in pH levels during cleaning can also stress goldfish. Make sure to check and adjust the pH level gradually if it deviates from the ideal range.

6. Improper cleaning techniques: Avoid using harsh cleaning agents, such as soap or detergent, as they can be toxic to goldfish. Use only gentle, aquarium-safe cleaning products.

7. Bacterial bloom: If the tank was not cleaned frequently or properly before, a sudden increase in water quality can stimulate the growth of bacteria. This can lead to an imbalance in the beneficial bacterial ecosystem and affect the goldfish's health.

8. Stress: The cleaning process itself can be stressful for goldfish, especially if they are not handled gently. Rapid movements or loud noises can cause stress, which can lead to a decline in their health.

9. Insufficient acclimation: Failure to allow goldfish to acclimate properly to new water conditions can also lead to stress and illness. Always float goldfish in a sealed bag in the tank water for at least 15-30 minutes before releasing them into the tank to allow for gradual temperature and water chemistry adjustment.

If you suspect that your goldfish are ill after cleaning their tank, take immediate steps to address the potential causes and ensure their well-being. This may include monitoring water parameters, providing appropriate treatment, and reducing stress factors in their environment.