Half gallon = 64 oz which mean this is adequate for someone in the 128lbs weight range. The formula is just a a guideline. One of the things that will tell you if you are well hydrated is the color of your pee. When well hydrated your pee should be from very light yellow to clear. If it's medium to dark yellow you need to drink more water. The darker the pee the more dehydrated you are.
The advice on the routine in my previous post still stands
The type of salt and temp can make a world of difference in how the SWF will taste. The light grey Celtic Sea Salt or pink Himlayan will be way mellower than ANY of the white processed salts. Doing the SWF tepid (slightly warm) will be waaay mellower than if done cold