When I bought my cory there was a sign posted NOT to use salt because it will kill them. I don't use salt, however, I have used it in the past when I kept goldfish.
The glass under the light may be cleaned with oven cleaner! I know, it is poison, but, you can wash the heck out of it when you are finished. Then I would run it through the dishwasher with salt as the cleaning agent, or baking soda. Then, rinse, rinse, rinse. I often wash items used for my animals and fish in the dishwasher using sea salt. It works very well. You can even wash the rocks you have, since they are rather large, use a colander to keep them together.
Sorry you are having such a hard time with your plants. I went for a lightly planted tank since I want it to look like a river or stream. I come from the NW and our streams have small gravel and rocks. I know the rivers where my fish come from are probably mucky, but, I don't want to look at muck.