Yeah so, odd thing that happened. One of my tanks (5 gallon) killed off 2 guppies. I could not figure it out... So tried 2 minnows. They died. I cleaned out the entire tank, threw out the rocks, plants - all that stuff. Cycled and all, I tried again. I thought "maybe it is the filter" so when it was ready, placed one guppy and my betta in there. In less than 15 minutes both went into shock - I removed them to my main tank, but sadly the guppy died.
So the tank was leaking some poison, obviously, and my betta (Spartan) lived through it. Just now the underlining of his kills went black, but he has no problems other than the discoloration. Would the poisoning even have decreased his lifespan?? Sure hope not. Such a fighter my little Spartan :p