Something is definately out of wack if you have a massive algae buildup in only a week's time. If you don't have any fish in the tank, here is what I would do:
1. Empty the tank completely and start over. Since you don't have that much time into it, then it might be a good idea to start fresh. This shouldn't be a big deal since it is such a small aquarium. It sounds like there might have been a phosphate/nitrate imbalance (possibly due to tap water if that is what you used).
2. Get some RO (Reverse Osmosis) drinking water from the store. Look for RO or Reverse Osmosis on the label on the bottle. I tend to use Deer Park drinking water.
3. If you are going to go with plants, then consider a different substrate. One of the benefits of having such a small tank is that you don't have to pay so much for the "good stuff". Normally I wouldn't say to ditch everything, but since I am suggesting a do over, then might as well do it over right.
4. When you get to the point where you can add fish after the tank cycles again, I would not use a pleco in the tank especially since you are going with plants. Plecos eat a number of different species of plants, and it might be better for you and the fish if you just avoid that entire experience. Go with some Otto's. They are great little fish and they will get the job done for you (for the most part). I have also have good luck with Rosy Barbs (not Neon Rosy Barbs). They tend to "pick" at other types of algae like hair and staghorn.
5. See if there are some other lighting options available for this setup. I have seen the built-in lights that the Eclipses use, and to me, they look to be extremely weak. If there is a way to retro fit the hood with some additional lighting then that might be the way to go.
6. Try to stay away from PH buffers. They tend to throw the phosphates out of wack and sometimes can lead to algae issues.
Are you using any ferts for your plants yet? That too might explain the new algae growth. Sometimes people get a little carried away dosing nano's with ferts, and it winds up causing an imballance which leads to extreme algae growth. The other thing is that when you add plants to an aquarium, and then you get an algae breakout, then that could be an indication that the plants are not consuming resources at the rate that they should be because of some condition within the tank, i.e. not enough lighting. Let us know what happens and keep us posted. Hopefully, your nano will be thriving in no time.