I still don't understand what you planted your plant into? Where did you get the soil? What does it have in it? The soil is very dense and I do not believe that it is going to give you the wet and dry cycles that the plant needs. The soil needs to be light enough so that as it dries out it pulls oxygen into the dirt for the roots. You really need to amend the soil with something like perlite so it is lighter and does not stay so soggy. Also, I don't think that one hole is enough. Put some more holes in the container. I like to have some holes around the perimeter of the pot at the bottom to aid in drainage.
How do you check your pH? If you add lime to your soil, you will probably not need the pH stuff. Also, I have never seen a product to adjust the pH that turned the stem white like this. I still suspect mold or the disease called damping off, although that usually happens with seedlings. Why are you giving it calcium? What else are you feeding it? Vegging plants also need P, K, and micro nutrients.