I wouldn't be too worried about it. There are two acclimation factors here:
1) Emerse to Submerse - the dwarf hair grass needs to acclimate to the submerse environment. Most of the plants (e.g., tropical) are grown in pots through the emerse environment. Dwarf hair grass is very finicky in that it will take up to 6 weeks before it fully hits off and starts to spread like crazy.
2) Nutrients/CO2 and Lighting Period - It needs to adapt to the conditions that you are providing. Ideally you want to provide 30 ppm of co2 (drop checker is green to yellow), dose a regular fertilizer that is non-limiting (e.g., Estimative Index) and give it a proper photoperiod of 8 - 12 hours.
You don't have any quick growing plants (stem plants) in that tank from the looks of it. I would not suggest that you go all out and start dosing a full non-limiting fertilizer regime. Most likely, you are going to end up with green water and tons of algae.
Also, it is common for plants to melt (cryptocoryne rot will apply here) if the parameters are incorrect. You did mention that it is a new tank and the substrate is fresh. Give it some time and let the system establish and then go from there.