IT is a Wrong way that many people use it as the original light in a tank with fish.
The best way is using the light with a filter or in a sump filter tank,if you do not have a filter that fits it,may be you can divide the fish tank two part with a Opaque plastic board,use the light in the part which the fish can not reach.but please make sure the water can flow over the plastic board,so that the light can kill the bacterial in the water.
Because as bait fish and other organic matter will produce, heterotrophic bacteria will multiply it immediately decomposes the organic matter,
the large population of heterotrophic bacteria caused a decline in water clarity.
For this case,you need a UV sterilizer light to kill the bacteria and make the water clean.
I suggest that you should use the light 3-4 hours once in 2-4 days.
But because The number of bacteria is mainly determined by the amount of fish feces and the water temperature,you should find the best clean time by your watched.
Features:
-Voltage: 110V
-Frequency: 50-60Hz
-Power: 7W(9.1inch),11W(13.4inch)
-Cable Length: 1.8m
-This sterilizer lamp can be matched or connectted with different pumps.
-Power Adapter: US Pin(with on/off switch)
-Split type design for high safety & fix with strong suckers. Firm and Reliable
Note: Plese DO NOT use this lamp as ordinary lighting,
DO NOT expose the fish directly under the UV light for long time,
Please install and place it in the filter tank or the other place that the light can not leak out.
Package Included: 1 x US Plug Aquarium UV Sterilizer Lamp
1X User manual

• UV Sterilizer light help to clean the water and kill the bacteria,such as Fish tank,swimming pool,pond,industry water processing, bio-pharmaceutical industry, cosmetics industry, semiconductor/optical, electronic technology, SUN, sewage treatment and so on.
• If you do not follow the Instructions,your fish will be hurts,Instructions:the best way is using the light with a filter or in sump Filter tank,if you do not have a filter that fits it,may be you can divide the fish tank two part with a Opaque plastic board,use the light in the part which the fish can not reach.but please make sure the water can flow over the plastic board
• 13.4inch 11 Watt UV light,Suitable for Freshwater and Saltwater,suggest that use the light 3-4 hours once in 2-4 days.
• Life keep up to 10,000 hours or more,Power Plug with Switch on/off,Suitable for tanks up to 500-gallons,Make your fish tank's water clean and clear.
• Promise to respond within 24 hours, 30-day money back or replacement warranty, and lifetime support guarantee.