Yep, adding that package to any tank will change the bios drastically. That is why I was thinking just water and sand (and maybe LR). Don't get me wrong about TBS, I just might try it some day. But there could be better ways to prepare a tank for "hit".
And the "hit" is not avoidable. Simply because many wild species cannot survive in a tank, regardless. Some other will die because of the instability. Most of them we probably can't see with naked eyes. Their processed bodies will just keep showing as nitrate in the coming days, weeks, and months. However long for nature to take its course.
Here is what I would do: set up a 75G with water, sand, and 30lbs of other LR for 6 weeks. Then order a 30lbs package. Wait 6 months, order another 30lbs.
It's a good point about the un-seeable die off. No telling how many microscopic creatures have bit the dust. Also, there is TONs of crab and snail poop in my tank. Tons. I just read that fish poo does not contain nitrate but what about snail and crab poo?