So, the thing about factory-iodized salt is that the iodine has a fairly short half-life. I don’t know how they add it to the salt, but I’m willing to bet that Himalayan salt has a more stable form of iodine, even if it’s less than the concentration of factory-iodized salt. What I’ve done before is use half-iodized, half-Himilayan salt for the sodium chloride portion.
If you can’t find No-Salt, you could use “light-salt”, which is half-sodium chloride, half-potassium chloride. Of course you’ll need to figure out the math for the rest of the recipe to balance it out.
I believe the purpose of the baking soda is to balance the load to the kidneys during fasts, and reduce the risk of kidney stones.
As far as non-food-grade epsom salt goes, I’m not sure. A coffee-filter can reduce large particles, but for smaller contaminants, you could try a carbon or charcoal filter if you have them. In this direction, you could think of the epsom salt as the first ingredient into the water, and then add the rest after filtration.
Edit: spelling