hi mate , i have kept many of theese fish and have some at the moment , if you stick to one fish the tank should be ok , i would prefer min 4foot lengh yours is about the min i would use for one , the temp should be between 18-23 deg but they will tollerate higher , at higher temps they become a lot less lively and there colours are not so good, i keep mine at room temp ( iam in the uk ) today there tank reads 24deg, give it lots of floating plant cover and a couple of caves to make him feel secure ,and he will be on show most of the time , they quickly learn who feeds them and learn to strike food as soon as it hits the surface , they are actually far better looking in real life than in photos , there is a lot more colours on them that camera does not pick up , you will not be dissapointed with one of theese fish , they are great but do not try and house anything else with him in that size tank , even a partner ,it will no work .
good luck finding a nice one , look for one with more blue in dorsal fin than the others in the tank , that is most likely a male and will colour up better than a female
cheers col