Kelvin ratings don't "combine." If you have 2 x 6500k bulbs in there, your lighting is still 6500k, not 13000k. That being said, yes I highly recommend you keep within the range of 6500k to 10,000k. Your 5000k bulb is close so that one may be okay (albeit a little too yellow for my liking), but I think that 2700k one needs to go. That's the spectrum you would use if you were growing fruits and/or flowers in a terrestrial garden.
I don't know much about the Eclipse tanks, much less their hoods, but I do think that 30w will be sufficient in a 20g tank, to be able to grow low light plants anyway. But you should make sure they are in the right spectrum. Pay little-to-no attention to marketing gimmicks that claim certain bulbs to be "for aquariums" or "just like sunlight" or whatever. Just simply go out there and grab some 6500k T8 15w bulbs. I personally tend to like blending 6500k and 10,000k in my tanks. It makes for a very crisp, white light, that is neither too blue or too yellow.
But this is just my opinion of course.