Calcium hardeness levels

Pool water should be maintained for bather comfort, and grout should withstand that water. Ideally, calcium hardness should be maintained between 75 mg/l and 150 mg/l. Incorrect Can you please help with this as i cant sem to get past the course onto the next level. I really cant find another answer than what i have put in so im very confused that this is not the correct levels for Calcium levels. Many Thanks