A friend of mine had to get rid of his female guppy and 3 young black mollies a.s.a.p., due to circumstances. I told him my tank was not the best place for those fishes, but he told me there was no alternative. So I said yes and went to him to get the fishes.
With a heavy heart. What future would these fishes have now... On the other hand, the tank where the fishes lived, had the same temperature as mine, so the shock would be smaller.
I found a very big guppy ("megagupy") and 3 black mollies and took them home. The fishes were moving fast, there was so much life in them, I've never seen that with my (now dead) own guppies!
I let the plastic transportbag float on the watersurface, added patiently some water from the tank now and them so the fishes could get used to this water, etc. While I was doing that, little guppy seemed to brighten up!
And then it was time to release the fishes in the tank. Big fun! They started to hunt for food (something the old guppies never did), didn't hide when I looked at them (or the cat!), and you could almost hear little guppy think: "wow, these folks are a lot better than those zombies I had to share my tank with!"
Little guppy behaved like a dog that meets another dog: she swum around and around megaguppy, "sniffed" her skin, and showed more life than she ever did before!
The new fish eat more in 1/2 hour than I have ever seen the last 2 weeks.
The first signs look hopefull! No stress, healthy behaviour, good eating and swimming, and bonus is that the little guppy reacts very well to her new roommates!
By the way, I also talked with my friend about the misfortune I had with my other guppys. He told me (and it isn't the first time I've heard this, it is also told in the comments here) at this moment there is a lot of bad guppys in the shops. They come from mass-breeders in Asia who are only in it for the money and don't care about health and good breedinglines. The results is a new generation very bad guppys who die young and can't stand the smallest stress (with diseases and death as a result). The (good) pet shops are worried about this developement.
My friend thinks that this generation of guppys will extinct soon, and when the petshops will get their guppys from other breeders, the problem will be solved, but that will take time.
He had this guppy (megaguppy) from a good pet shop months ago, and this guppy is so completely differend than those yellow-and-grey Asian guppys who behave like zombies and die like flies... This is the way a guppy must be: cheerful, busy, not so stressed, and curious! By the way, megaguppy is expecting...!
About the black mollies: I don't know if I keep them in the future. My tank is small and I have to make a choice to avoid a overcrowded tank. But that is something for the future. First let me see if my new fishes stay alive!