Once again trying to think it out...is nitrate a chemical or a bacteria? I would think bacteria since it "feeds" on nitrite. If it is a bacteria then it should be able to be "killed"...correct?.....
No worries. I've spent lots of time talking to fish people and reading up on this since chemistry is not my thing.
Nitrate doesn't feed on nitrite, it is the byproduct of nitrite. Here's the way the cycle works, and I find it most useful to consider the bacteria as what it is: a microorganism that consumes food and excretes waste.
When you feed you fish, they excrete ammonia, which would spoil their water and kill hem but in nature and in a well established aquarium filter (or substrate, technically--let's just stick with filter since that's where most of ithappens), there are beneficial bacteria, which consume the ammonia. As they consume the ammonia, they excrete nitrite. Fortunately, these colonies of bacteria also eat nitrite, so as the water continues cycling through the filter, it consumes the nitrite and the excretion is nitrate. Nitrate can make fish sick and vulnerable, but does not kill them at most levels. Unfortunately, no bacteria eats the nitrate, but plants use nitrate as fertilizer, so lots of plants can lower nitrate levels. Otherwise, there is nothing in the ecosystem of the aquarium to consume nitrate, so you have to remove it via water changes. So, consider the nitrate bacteria poop (for lack of a better word), but not bacteria.
It all starts with food for the fish...then,
Ammonia=Fish poop and Beneficial Bacteria A food
Nitrite=Beneficial Bacteria A poop and Beneficial Bacteria B food
Nitrate=Beneficial Bacteria B poop and plant food
That's probably not the most scientifically precise description, but it is how I have been able to explain the nitrogen cycle to friends and family when they ask.
Fortunately, my Rocky Mountain tap water contains no nitrates of its own, so a small change can make a big difference. Unfortunately for the OP, her tap water has lots of nitrates itself, so she has to change far more water as she is simply removing water with 160 ppm (parts per million) of nitrates and replacing it with tap water that has as many as 60 ppm. Ideally, she would like to see her nitrates somewhere between 10 and 40, but she will have a heck of a time achieving less than 60-80 even with her diligence in water changes. I hope this helps explain. Let me know if you have any other questions!