OK, I've two suggestions.
First, ask them next time you're in the store what exactly is in the water you buy (unless it has this on the label). I would bet there is some dissolved mineral in it to add some hardness. As others will tell you on this forum, "pure neutral" water is not suitable for fish because there is nothing, literally, in it. Fish need some minerals (just as we do) and they get these from what we feed them (minimal) and from the water they live in. Fish absorb water through their cells by osmosis, which is their equivalent of our drinking, and they adjust their internal pH, salinity, etc. to equal the water they live in. This is why fluctuating pH and hardness is so detrimental to fish. Anyway, to get back to the water, if there are minerals in it there will be a buffering capacity, and I would leave it alone.
Second point is that for the fish you list, a neutral to alightly alkaline (basic) water is OK, so I would leave it alone. Swordtails and platys are livebearers, and all livebearers prefer and are healthier in slightly alkaline water, anything (stable) from pH 7.0 to 8.0 is fine. Albino corys come from slightly acidic water but they adapt very well to what you have, provided again it remains stable. White clouds are not really tetras (stores often label them as such, but they are not at all related to the "tetra" of the characidae from south America) but are minnows from the White Cloud Mountain streams in China; they are fine in your water, as are Glofish which I assume are the genetically-modified forms of zebra danios. The two true tetra species can also manage quite well.
It is a common fallacy that the best aquarium water is neutral, pH 7.0, and aquarists sometimes go to great lengths to achieve this. I cannot think of a single fish that lives in a neutral water in nature (there may be some, I just don't know of them), mainly because such water is anything but natural. Vegetation (plants, trees) and soil add tannins (acids) to water, or limestone rocks make it alkaline, and so forth. It may seem sensible to provide neutral water for a mix of fish from varying waters in nature, but the problems caused by fluctuating water parameters are far worse on the fish than getting them adapted to a slight variation that remains steady.