What kind of light do you have? If it is an incandescent fixture you might be able to swap out the bulb with a CFL bulb (6500K maybe 13w). They run cooler than incandescent bulbs. However, the 13w CFL might be too much light for that size tank.
You should be fine without ferts. I have a shrimp tank with crypts and moss and the the crypts get root pellets (which won't work too well with the under gravel filter) but the moss thrives without ferts.
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