I was thinking about buying a low light plant package from That Fish Place and was wandering if I should buy some flourite or other kind of substrate to mix in with the regular stuff I have.
Hiya 85rbpbro, welcome to MFK, I don't think it would hurt but I am sure those who know plants better than I will clue you in. I usually use small pots for my plants.
You would have much more success with special plant substrate, generally what people like to do is have layers: first layer of special plant substrate and second layer of either gravel or sand.