I am a beginner, and I think I already have a problem!

Help! I just noticed a white powdery "frost" on the top of the soil with my tomato seedling. It is a "Little Mama" tomato seedling (seed purchased new this year from Burpee) in a "Burpee Ultimate Growing System." It has both peppers and egg plants for neighbors. Looking back, there was an 8-Ball Squash in the same cell previously (although washed and rinsed well between use). There is another seedling of the same type directly adjacent to this one, and that one has a little of the "frost" also. I used the Burpee growing pellets for medium, and I don't use any fertilizer at this stage. The seed tray has been on a warming mat due to peppers also being in the same area. These are in my basement under fluorescent lighting (because our winter just won't go away!) and the soil is constantly moist due to the functionality of the seed starting system. At this point, the seedlings themselves visually appear unaffected.

What should I do? Should I simply pull everything in the affected cells and closely monitor the rest?

I attached a photo for a visual.

Thanks in advance!