Commercially farmed fish are more tolerant of different water conditions because they have adapted over a number of generations.
My LFS has exactly the same water supply as me so the fish will be fine
We have all seen these posts on our very own forum...
Today I went into my LFS and on a whim I asked if they had any wild caught cardinal tetras. I had been speaking to the "manager" for a while so he had already sussed that I knew a bit about fish. This is a reputable UK chain that is an aquatic specialist.
LFS bloke: "Oh yes, come this way. These arrived direct from Brazil 10 days ago".
Me: "Wait a minute, this is the hard water section, shouldn't they be in the soft water section?"
LFS Bloke: "Yes that's where we put them when they arrive but we have to harden them up to deal with the local water innit? Once they are ready for sale we move them into this side"
Our local water supply is at 16dGH. The Negro is at 0dGH. I have no idea how long it takes for them to arrive in the fish store after being removed from the river, but I would be very surprised if it was a month. So in less than one month wild softwater fish have magically been turned into hardy fish suitable for water that you can walk on