Beginner Gardening: Matina Tomato plant problem?!, 1 by HollysPlants

HollysPlants wrote:
Hi everyone,
I have about 20 matina tomato plants I've grown from seed using soil pods and transplanted to larger pots almost a week ago. They have no moved from the window (have rotated every other day) since I started them. I have about 75 plants in total there and today I noticed this plant and the surrounding soil has a white cotton-y appearance sitting on top of it. I watered them all two days ago and they've all been fine except for this single plant. Usually I water every single day - just a little bit - and then they are dry the next day so maybe I overwatered a bit the other day? I have added a photo of another matina plant of mine for comparison.

Please let me know what this is and what I can do? Thanks!