The Green Killing Machine 24W Internal UV System Bulb should be replaced every 6 to 9 months (assuming it is used constantly). 

This Green Killing Machine 24W Internal UV System Replacement Bulb is very easy to replace as you just replace the entire housing for the UV. 

No need to mess around with caps, gaskets and quartz sleeves when replacing your bulb. 

For the Green Killing Machine 24W Internal UV System with Power Head. 

Manufactured in EPA Est # 093568.