A common salt recipe for vegetable ferments when the brine is made naturally from the water contained in the vegetables:
3 tablespoons granular salt per 5 pounds of vegetables.
A tablespoon of salt measures about 17 - 19 grams, depending on how "fine" the salt granules.
In metric units, that is: 52 - 57 grams salt per 2.27 kilograms veggies.
You have 5.0 kg of cabbage. Therefore, a salt amount should be:
(5.0 / 2.27) * 52 = 114.5 grams salt: (about 115 - 125 grams range).
However, you are actually using 200 grams of salt, which is more than enough.
Amazon lists several salt brine hydrometers that can used to measure actual salt brine concentrations.