The bacteria starter packs... I would avoid them. They are hit or miss at best. Any product with live bacteria has a high chance of not being stored properly (i.e. temps to high or low) which would then kill off any living bacteria.
Nitrifying bacteria are aerobic anyways... so they aren't going to live for long in a sealed bottle.
Petsmart or Petco carry the API freshwater master kit. It is also widely available online.
Unfortunately, the LFS
, and especially the big chain stores, are not the greatest places to get advice. They perpetuate a lot of myths and untruths... we see it all the time. The advice here is generally pretty dang good, and comes from people with a lot of personal experience. Many of the employees at these stores have likely never started a tank of their own, and don't have an understanding of the nitrogen cycle, which is about the most important biological thing happening in an aquarium. Rather than go with what works, they tend to recommend chemical treatments (like the ammonia remover stuff they sold you). The only chemical ever needed for healthy tank is a good dechlorinator, like prime. Anything else is basically a band aid fix. Problems need to have their root caused addressed, rather than a chemical solution.