Method 1: If you want to remove the scale in the fish tank, you can wipe it along the inner wall of the fish tank with a clean bath towel.

Method 2: When cleaning the fish tank, wipe the inside of the fish tank with salt (excluding iodized salt) to remove the hard scale, rinse with water and then put the fish back into the tank.

Method 3: Pay attention to maintenance at ordinary times. Might as well buy a filter.