T8's would be low lighting. You could grow most val's (they are often sensitive to liquid carbons), swords, crypts, water sprite, pennywort, along with anubia's, java fern's, and bolbitus for tying onto rocks and driftwood.
Liquid carbons such as Metricide 14 and Excel is fine for discus. I just do not suggest using them at doses above 1ml for every 10g daily. When keeping discus in a planted tank you have to find a good balance for both plants and fish.