When first setting up a planted tank, you need to "overstock" with plants or algae will compete. Once plants are established you can arrange them better or remove the cheap ones and put in nicer ones.
Now that your plants are actively growing and well rooted you have to keep an eye out for defiencies. Leaves turning yellow, getting clear, melting,...etc. This will tell you how much you need to dose with nutrients, keeping in mind that more lights means more nutrients and more pruning/maintance.
With T5 lights you have 2 options lots of pruning, CO2, and nutrients, or reduce the lights some/raise them and less pruning and nutrients. This however, may limit you to certain plants that do not require as much lighting.
...The green on the sand is most likely Blue green algae which is actually a cyanobacteria. It likes the silica in sand and can be treated with eyrthromycin since it is a bacteria.