Heya... What a cute tank! I've been tempted in the past to get a hex, but at the time, it was very difficult to find any type of fluorescent lighting for it. Well, if I were you (and of course I'm not), I would try to stuff more plants into the tank and just do away with the air pump. This way, the plants will do better without the air bubbles driving out the CO2 and the fish will get enough oxygen from the healthy plants. You may also want to add fertilizer. See how the newest leaves are growing out sort of small? That's a pretty sure sign of nitrate deficiency. Of course, with that amount of lighting over such a small tank, ferts are going to get used up really fast - if not by plants, then by algae. DIY CO2 would be helpful, too.
Another thing - thought I'd suggest Heterandria formosa for a non-heated tank. They're small livebearers with the common name "least killifish" (misnomer - they're not really killies). I've been told that they can easily tolerate temperatures down in the 60's and even 50's. Some guy in SF said that in winters past, he's left a bunch of them in a barrel outside on the deck and they were fine. The water typically got down into the 40's. I've kept white clouds in an Eclipse System Three, and they just looked so out-of-place, trying to zip around at breakneck speeds; I think they're not really suitable for tiny tanks, but you may have a different experience. Amano shrimp are good for non-heated tanks, too. They're not a tropical species so they actually prefer slightly lower temps.
What are those floating plants?
Oh, also, there are plants that actually grow better in cold water. Some of these are Lysimachia nummularia (regular and 'aurea'), Cardamine lyrata, Hottonia palustris, Anacharis, and I think the Hydrocotyle spp. They also need quite a bit of light, but I'm reasonably certain that you have enough, there
I love the rocks and gravel you use. They really make me think of the desert, with their warm tones.
It's a really sweet little set-up you've got! I might consider getting one for myself, but I'm already in the planning stages for a non-heated 4-gallon 'long'. Would love to see what your hex looks like a few months from now... Great start!