Xiphophorus variatus, true variatus platies, are not cold water fish, ever. The LFS often will label almost any platy as a variatus, so you cannot go by the tank labels. Almost never will you see a true species of any kind of platy in the LFS but instead what you see will be platy/swordtail crosses. X. variatus and X. helleri are among the most common ancestors of most modern pet shop platies and swordtails, yes both of them, but a true X. variatus is something I have never seen even as a wild type livebearer specialist. It just does not show up in pet shops and seldom shows up even in the specialist locations that I frequent. An endangered species of goodeid is easier for me to find.