Plants not thriving

This is my first planted tank, and I am having problems with the plant, This is a 29gl newley cycled tank. I have about 10 plants currently they keep sprouting new stalks but the older leaves are brownish almost burnt looking. I talked to the owner at my lfs who has more plants then any other store in my area. He said that I should avoid using water conditioner because it is blocking the leaves receptors. He claims that he does not condition his water at the store at all. We are on the same city water grid so it is the same water for me as it is for him. However i am nervous about not using the conditioner even if I let the water sit out for a couple days in buckets. Any thoughts or suggestions to help get my plants flourishing? I would appreiciate it. Side note: parameters are all reading 0, water temp 80, running a T5 6700k. I have been using stresscoat+ for water conditioning and flourish (recomended by the lfs owner) for plant food.