If you know how to take care of him, then buy a heater, even a used one if need be. And if you don't want to follow sound advice, then why bother asking? FH like most designer fish are overall genetic weaklings, and any form of stress, especially in a young FH such as this can weaken their immune system, which can lead to further health issues. Running a heat lamp over it's tank 24/7 is a bad idea for the various reasons already stated. I expect your next thread to be HELP ASAP - My new Flowerhorn is Sick!