When you call it a "little one" that leads to me thinking it's undersized; what are you trying to accomplish running U/V?
U/V must be mounted in a manner that forces the chamber to stay 100% filled, which generally means the inlet/outlet should be facing vertically. Your unit has both facing straight down. If this returns right back to your sump (versus through a reactor or up to display) chances are the chamber is not full which can cause quartz sleeve failure. Of course any portion of chamber not filled won't be doing you any good.
How did you measure this?
U/V is incredibly effective if installed and maintained properly. It's important to be aware of it's uses, however. Just like every other piece of equipment not all units are created equal, most should be avoided.