How to keep the water in a hydroponics tank warm?

I recently got an Aerogarden Harvest Elite (6 pod) and also another off brand with 12 pods, so I'm new to all of this. I soaked some seeds and put them in the pods in the 12 pod one for now, but the temperature reads 60 degrees F which seems a bit cold for most of my plants (tomatoes and peppers). I'm worried they won't germinate and these devices already come with grow lights so I won't be able to put a heat lamp or whatever above them. And I do not have a warmer place that I can put them in my place. Is there anything I can do to keep it warmer? I was suggested a seed heating pad or a small aquarium heater but will those be sufficient enough? Plus the pad won't be against soil pots or whatever, it will be under a large water tank and I am not sure if a aquarium heater will fit inside the water tank. Thanks!