Yellowing Baby Grass

I planted new grass in a portion of my new lawn a month ago which had grown up in hay instead of grass (probably due to being made out a truckload of hayfield loam). I hand weeded the patch until it was bare, let it sit, weeded some more, and raked it. I did not use roundup on this particular area to kill the hay since it didn't work when I tried it earlier. The grass came in very nicely, but now I've got a patch of the new grass developing where the all the tips of the blades are yellowing.
Is the problem is that this particular patch probably got an overdose of starter fertilizer? Or could this be because the soil is very wet--we had a ton of rain plus I watered a lot to get it to germinate. Even after almost a week without watering, the soil is quite moist and there is quite a lot of moss developing.
How can I determine the cause--fungus or too much starter fertilizer?
And whatever the problem, is there anything I can do to save it? Will it recover on its own or will I need to reseed this patch yet again in the spring?
--Jenny
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