I don't know i have never measured water temps, when the plants are small and there is no canopy to shade the tanks the water can become luke warm very quickly i would raise the lights, this is the only time i would have to think about the temp of the res
i prefer it to be cold which it is most of the time, i put my hand in it to feel how hot it is from time to time its mostly almost as cold as when it comes out of the tap
i add water every day or every other day with larger plants as they drink so much that keeps it cool