My comments on the several issues raised in this thread, starting with the original poster's (Bob).
First, on stress. Stress is, well, stressful, and that weakens the immune system of fish just as it does humans. But a minor temporary stress is not the same as something permanent [watch out...more on this in a moment
]. My fish all move under plants or the opposite end during water changes, but you can't use this temporary and minor stress to counter the tremendous positive benefits of water changes. Some fish do seem to get used to them, I have had fish come up and nibble the hairs on my arm when I've been working in the tank.
A more serious stress is that being caused by the number of this species. I realize you are getting 3 more, good...I'm just noting that the stress of only 3 is more significant than the stress of a weekly water change.
In any and all freshwater aquaria, a water change should be carried out every week, without fail. There is just too much data out there on the mathematics for anyone to advocate anything less. However, it is true that some factors can mitigate weekly down to less often. Live plants with a small (moderate) fish load. A very large aquarium with few fish. One source I read mentions a 55g, well planted, with 6-7 neon tetra as being "balanced" to the point of not requiring water changes. Most of us have far more fish per volume that that, plants aside.
The volume changes is also somewhat related to the fish load and tank volume, and again live plants. I do 50% of my tanks every week, and have done for 15 years. I am absolutely convinced of the benefits solely from the response of my fish. With a 10g, and given this tetra I would do 1/3 to 1/2 the tank weekly, and when you have 6 tetra, definitely 1/2 the tank. I am assuming the parameters of the tap water are reasonably close to the tank. [We can discuss this further if you ask.]
The water changer Gwen mentioned is the way to go. With a small tank, a manual one is fine; I use this on my 10g. If you get larger tanks, a Python is a good investment.
Last on this, why change the water? Because there is "crud" in the water that you simply cannot remove any other way. Stuff that no filter can handle. Fish urine, dissolved waste, pheromones released by fish and chemicals by plants...all these have to be manually removed. Allowed to build up, they can be very detrimental. There are no tests for any of these; but believe me, they are there, unseen and undetectable--except by the fish that have to swim around in all this crud.
Someone mentioned nitrates; while water changes are one good way of keeping nitrates in check, it is not only for nitrates. My tanks have zero to 5ppm nitrates max, but I still do 50% water changes weekly.
Moving on to Ridewithme38's question. Use water from the cold and hot water taps, mixed to the approximate temp of the tank water, perhaps just a tad cooler. This works for most fish; there are only a very few that should have equal or slightly warmer water added. If we're dealing with a 10g and using a pail, get the water the approximate temp, then squirt in the conditioner and swish it for a second. Conditioners work immediately to neutralize chlorine, chloramine, etc. No need to wait.
If you have larger tanks and use a "Python" gadget, get the temp approximate at the tap then switch the Python to fill the tank. Squirt the conditioner into the tank as it starts to fill. I've done this for 15 years.
Hope that helps.