During the last few hours of the night I put the white eclipse bulb back in that came with the hood and, well, yea... the fish were definately more active. Maybe it doesnt harm them but they just dont know how to respond to it. I'm sure its very different than their natural habitat. I think we're gonna keep the white light in. We (my family) were all very excited about the idea of this tank but it flopped and we all ended up very dissapointed. We are enjoying it alot more with the white light. Just looks more vibrant and active. To anyone thinking of playing around with a 10g tank with a black light... dont think Id go for it... tho I must say that a smaller tank really might look good for something such as the beta.