Dying fish after long night with lights turned off

[ToOthleSS04]

I'm getting so frustrated, ever since I bought a new neon lamp my fish keep dying after a long night without any light source. I thought it'd be a good idea since fish don't require lights turned on always, and also becuase of money, but ever since that my fish keep dying without no reason.. this morning I found my cobra mosaic male guppy dead on the floor of the tank... Is it water parameters? Is it temperature? Is it stress? Please help, I don't know what to do!

 

[Ouse]

Hi, please use the emergency template.

...and no, it can’t be because of no light at night.