That looks like an
Aquarium UV sterilizer. They can be used for zapping (using ultraviolet light) free floating parasites and algae. I think you'd only notice a small improvement in maybe reduced algae growth. Hard to tell in established tanks how effective they are at zapping parasites and they need a very slow flow through rate for killing pests/parasites.
You'll also need some sort of pump to move the water through the unit, and you'll need to keep the quartz sleeve cleaned (monthly) and the UV bulb will need replacing between 6 months - 1 year.
Mike
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