If the chick starter isn't medicated any high protein feed will do. Calcium deficiency isn't the only cause of soft shelled eggs. Illness, heat stress and too much phosphorus to calcium ratio can also be factors.
http://www.alltech.com/sites/default/files/alltech-egg-shell-quality-poster.pdf
I'll have a look through this too - thanks for the info. I'm having the same problem as @AussieChics . I was feeding grower with grit and crushed egg shells on the side and my ISA brown started laying really soft 'shelled' eggs. I'm now feeding them all layer feed until she recovers, but as it's just the one hen maybe it's being caused by something else.