This is a bath sea salt in a 1000 g pack, and the main active ingredient is sea salt itself. There is no single right dose for every tub, so the practical way is to start with two or three generous handfuls (roughly 50–100 g) in a standard bathtub. On your next bath you can adjust the amount based on how the water feels. A stronger mineral feel is easy to add, but it is hard to remove salt after it has dissolved, so a smaller first bath is a sensible starting point.
Add the salt while the water is running so it dissolves evenly and does not settle as a gritty layer on the bottom of the tub. The temperature depends on the effect you want: the product information says that a warmer bath is commonly chosen for relaxation and muscle ease, while a slightly cooler bath feels more toning and refreshing. So use comfortably warm water for a slow evening wind-down, and a moderate or slightly cooler bath when you want a fresher feeling after physical activity or a long day.
Very hot water is not necessary and can leave you feeling drained, so keep it at a level where you can sit comfortably for 15–20 minutes. If your skin is sensitive, irritated, or has active flare-ups, start with a smaller amount and a shorter soak, and skip the bath if the skin is damaged. If you are unsure whether hot or mineral baths are suitable for you, ask a medical professional for individual advice.