Rosy reds are temperate, not cold water, so they're good at most temperatures (50-85 preferred, survive 32-100). Good things to address about keeping fish at the wrong temperate though ):Rosy Reds are a cool water fish (usually kept on a separate system in fish stores with the goldfish, from the tropical fish.) They prefer their water from about 60/63 degrees F to around 75ish. I wouldn't keep them with any fish that prefer water temps in the 80's F, as the warm temps can make cool water fish more disease prone. You can lose them to heat stress the closer you get to 80 degrees, for various reasons. If you notice them gasping at the surface, the water is probably too warm and doesn't have enough dissolved oxygen in it. Just something to be aware of and keep an eye on. There can be many other things going on with any fish species from illness to parasites to poor water quality. But typically the warmer the water, the less the oxygen for the fish to breathe is in it and warm water fish need fairly warm water ( with more water circulation to grab oxygen from air and dissolve it in water) and cooler water loses less oxygen from evaporation and can sometimes tolerate less agitation of water in general. Where I live in SD, farmers will buy rosy reds/ goldfish/feeder guppies and toss a bunch in livestock ponds to eat algae and mosquito larvae, so their cattle/sheep or horses have few mosquitoes preying on them. Obviously these ponds are at whatever the ambient water temperatures are at and some live/some are prey to frogs, turtles, birds etc. Sometimes pelicans drop larger fish like bass or sun fish in the same pond. Nature balances it out and hopefully you have fewer mosquitoes biting people and livestock, spreading mosquito borne diseases.