They look OK to me. Are they getting full sun? They'll appreciate as much light as you can give them.
For what it's worth, I never fertilize my seedlings. Fertilizing irises is, IMO, the first step in a cascading series of events that end with rot. The closest I come to fertilizing is adding a fresh layer of compost every three years as I rotate through the seedling beds.
That being said, potting soil has a very limited amount of nutrients in it. The seedlings will only be happy in there for a few months. After that, they'll either need to be fertilized or planted in the ground. I try to get seedlings out of pots and into the ground within four months or less.
