Do you have a heating pad laying around anywhere? Once I had an issue with a 1.5gal and not having a suitable heater. So it was suggested to me on here as a fix until I was able to get one, to use a heating pad. Take the pad and then either sit his bowl on top of it or you can try taping it to the side. this really depends on the size of his tank. You are going to have to get a thermonitor to keep a close eye on the temp. Which can be found at a lot of stores for around 2 bucks or so. Set it on the lowest setting at first. If it still is not putting the water temp into the recommended range, try medium etc.