Fishle,
Funny thing about fish boards, and even your LFS... for each question, there seem so to be an infinite number of answers! Several conflict each other... Example? I've had people tell me that a planted tank is great for cycling, and another experienced person tell me that they never cycle with plants as they use up ammonia and prevent the bacteria from taking hold. I've seen one source recommend a salt bath for ICH and another say that it's ineffective and a myth. The moral is, for any question, there seems to be an infinite number of answers... it's just some are just bad advice.
With Bio Spira is really is best start with a decent amount of fish, you just bought enough ammonia to help cycle, say, a 1/2 of a full load(just a guess) and you stocked it with one fish. He's not enough to keep the large amount of bacteria alive! So they start to die off the support that one fish, then you add more fish, and they have to "culture" on their own in order to catch up... in another mini cylce.
Now, adding a few fish at a time is a good idea when you're doing a regular fishy cycle(once it's cycled) It's sort of the opposite, you've used one fish to establish a cycle with just ONE fish... then you add two more, and give it time for the bacteria to catch up.
While this doesn't solve your problem, it doesn't help you in the future.
I'll tell you this: I don't think you killed the bio spira, I think you delayed it a bit. If it were me, I wouldn't panic unless your ammonia started reading above 1ppm with no nitrites. HOWEVER, it never hurts to buy more Bio Spira if it makes you feel better.
I hope this helps!