Cleaning a fish tank is an important task to maintain the health and well-being of the fish. Here are some general guidelines for cleaning a fish tank:

1. Remove the fish: Before cleaning the tank, use a fish net to transfer the fish to a temporary container with water from the tank.

2. Clean the decorations: Remove any decorations, such as plants or rocks, and wash them with warm water. Avoid using soaps or chemicals, as they can harm the fish.

3. Drain some of the water: Drain about 20-25% of the water from the tank, being careful not to remove too much at once. This will also help you to remove any debris that may be at the bottom of the tank.

4. Clean the tank: Use a algae scraper or a sponge to wipe down the inside of the tank, paying special attention to the corners and the back of the tank.

5. Clean the filter: The filter should be cleaned every 2-4 weeks, depending on the size of the tank and the number of fish. Rinse the filter media with tank water to remove debris, but don't use soap or detergents.

6. Add fresh water: Once the tank is clean, add fresh water to the tank, making sure to treat it with a water conditioner to remove chlorine and other chemicals.

7. Return the fish: Once the water is at the same temperature as the temporary container, return the fish to the tank.

It's important to note that the frequency of cleaning a fish tank depends on the size of the tank, the number of fish, and the amount of debris generated by the fish. A small tank with a few fish may only need to be cleaned once a month, while a larger tank with many fish may need to be cleaned every week.