I really don't understand all this misinformation which, after reputable botanists and biologists point out its inaccuracies, still gets bandied about. [And the reference to reputable is not meaning my little articles
]. Only a month or so ago I read again in TFH about it being impossible to grow plants with less than 2-3 watts per gallon.
Anyway isimek, on your most recent point first, you should fertilize from the day the plants go in the tank. Plants grow by photosynthesis, and to do this they must have light and nutrients (17 in all, some are more critical than others). In a new tank there will be no organic waste, so even fewer available nutrient sources. A good comprehensive fertilizer once or twice a week is advisable. I recommend Seachem's Flourish Comprehensive Supplement for the Planted Aquarium
. I have been using it for nearly two years now, and many others here also use it. Make sure it is exactly this one, as there are several different products in the Flourish line. I would start with twice a week (the dose of Flourish is very small, for a 55g about 3/4 of a teaspoon is a dose, twice a week); with the brighter light you have this will be needed to balance, or algae will proliferate as others mentioned.
Back to the light issue, two T8 tubes over your 55g will be more than adequate. One full spectrum (around 6500K) and one cool white, or two full spectrum, up to you. I have a series of "sticky" articles at the head of this section entitled "A Basic Approach to the Natural Planted Aquarium" that might interest you for background info, and in Part 4 on lighting I explain the benefits of full spectrum and cool white, also how algae takes advantage, and fertilization is in Part 2. If you want to see the results of that approach, check out the photos of my aquaria under "Aquariums" below my name on the left.
You have a very beautiful aquarium, nice work there.