Fire bellied toads tank options, Help?

I just got two fire bellied toads and I have them in a 15 gallon with mainly water (about 3-4 inches deep) and I have a rock that I got from petsmart that takes up about 30% of the tank. I have brownish gravel and a repto filter, a couple fake plants and a thermometer, its about 64 degrees in there, is that bad? And I'm thinking about going all repto dirt and having a water dish big enough to put the filter in, Should I or no? I feed them crickets witch they love, I tried worms, and it's a negative.