I am setting up an aquarium and I was wondering if fresh plants help the alkinity and hardness of the water.?

Answer 1

Fresh plants do not affect the hardness or alkalinity. Decomposition LOWERS pH,it does not raise it.
Also there are very few plants that do well in moderately to very hard water(425 ppm or higher). Luckily the ones that do are easy to grow. For openers try the non-rooting plants like Java Moss or rhizome growing plants like Java Fern or Anubias sp.
Not many plants will do well in a newly set up tank either. They seem to prefer one that's well cycled and stable.
When choosing plants look closely at the water,temperature and light requirements for each specie,and if you can't provide all of the required factors,save your money. Plants can't be cheated.