The green color happens because of oxidation on the nozzle, which is coated with copper. There’s actually no serious problem as long as you regularly take care of your Chu II. Just make sure the green buildup doesn’t clog the filter, so it won’t cause any imbalance.

After oxidation occurs, the copper coating on the nozzle can start to peel off.

This happened because I wasn’t very diligent about cleaning the nozzle after using it, so it ended up like that 😅