The Anti-Biofouling Copper Guard can be used in addition to the standard electrode guard for protection against biofouling during deployment. The anti-biofouling guard uses copper to reduce biofouling, while still allowing proper water flow to the sensor.
Copper protects the logger by interacting with the chemistry of the water in which it is deployed. This reaction is an oxidation-reduction reaction that produces a patina. The patina depends on what specific chemistry is present, as well as depth, temperature, etc.
The patina should not affect the ability of the guard to protect the logger; however, if the logger is conspicuously gaining more fouling, it may be time to replace the guard. The guards' ability to protect the logger relies on the copper getting consumed.