Leaves as they age will often develop scars and damage but it isn't always possible to know the cause.

In this case I would need much more info - what is your soil mix, is the white stuff perlite, what have you fed them if anything and how often, how often do you water and how much, how old are the plants, are there any signs of insect pests, are they indoors or outside and if indoors have they been outside, etc.?

The issues of NPK are very different for seedlings than for plants in the garden and NPK is not the only issues when it comes to fertilizer. So which are these - seedlings inside or plants in the garden.

Have no idea what UN32 or AZ Best Tomato food are so can't help you there other than to say neither are common fertilizers for tomatoes. Miracle Grow, diluted to 1/4-1/2 strength is often used on young seedlings but it is only one brand of many available.

The goal is to use only a balanced fert with a ratio of approx. 5-2-1 or close and that also contains micronutrients.

Hope this helps.

Dave