UVC filter wattage Aquarium vs. pond

[kilnakorr]

I was just looking through various UVC filters (inline types), and wondering why there is such a big difference in bulb-wattage per liter for aquariums and ponds.

Examples:

Aquarium UVC:

9W - 300-500 L
36W - Up to 3000 L

Pond UVC:
18W - Up to 9000 L
36W - 18000 L

Flow rate, reflectors matters, but I find these differences remarkable. I would argue that flow rate is often less in a 500 L aquarium than a 15000 L pond, so UV exposure time would be greater running any of these in an aquarium.

Anything I'm missing?

 

[sparkyweasel]

Aquarium ones are to control various pathogens, pond ones are to control green water, ie planktonic algae.

 

[kilnakorr]

Aquarium ones are to control various pathogens, pond ones are to control green water, ie planktonic algae.

Well, most aquarium uv units are just clarifiers although the companies call them 'sterilizers'.
So they do the same job.