It is good practice to change anodes regularly, even if there has been little corrosion.
Several alloys are available which comply with the U.S.MIL American standard, such as type 18001-H (J-K), characterized by the addition of cadmium and aluminum. These are ideal for use in sea water, but also used in lakes and rivers.
You can also get a strong anodic behaviour from zinc with a high purity (99.995%) without the addition of other elements.
Use with temperatures that exceed 55 ° C is not recommended.