Avel never the less happy they are and as said breeding well, I prefer 20-25c but every year I have to spend my days in the cold weather and yet I survive ok.Hmm there's something that is over adapted to differing water conditions : it is atavism.
To be happy and thrive livebearers' water should be pH 7.5-8.5 with a 15-30 dGH water hardness.