I just realized that my most used tool in ranchu keeping is a fine metal mesh strainer, the one commonly used in the kitchen. The strainer that I have is 4 in (10 cm) in diameter and is made of staines steal.
One main use is to rinse and drain bloodworms. I usually thaw bloodworms in the cup of pond water and rinse under the running faucet in the strainer. Very convenient! I also use the strainer to skim the pond surface from anything floating. Especially after feeding bloodworms, as their undigested casings will float to the surface.
It is very easy to clean and sterilize!