[freydo]

you could, but your plants will show signs of nutrient deficiencies eventually, such as yellow leaves, holes in the leaves, etc.

you say you have high light plants in a ultra low light tank, without proper nutrients, they won't do very well. if it's cost, then i would suggest going with low light plants, such as crypts, swords, etc.

just check out the plant finder for the plants that suit you best. good luck!