Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Even if the 'wrong wavelength' was not a problem, you would have the problem that the UV won't penetrate very far into the water.
In a UV sterilizer the water is routed through the system so that it is exposed to the UV in thin sheets. This exposes the organisms (algae, single celled parasites, disease organisms) to the full strength of the UV, so it kills them.