They should be on starter/grower or if available in your area just grower.
If you are feeding anything other than the grower, you need to supplement with grit.
Keep them on the starter/grower until about 20 weeks or when you get your first egg. Then you switch to layer, either crumbles or pellet form and supplement with crushed oyster shell.
If you are going to continue to offer the scratch you described then you are definitely going to need the grit to help them digest the seeds.