Hi Danni,

I'm sorry to hear about your tomatoes, it's beyond frustrating and heartbreaking when you put that much into your seedlings and then things go sideways. 

As you've probably seen elsewhere online, oftentimes the curling leaves indicate a stress, usually water, fertilizer, or temperature related. This would appear more likely water or temp related since you didn't add any fertilization on this last round. I would first examine whether you think you've increased your watering enough as the plants gain size. Are they drying out too much in between or staying too wet without the roots getting enough oxygen? 

The next culprit could be your light. Are you moving your light upward as your plants are gaining height? If too close, the plants will lose too much water too fast and you could see leaf curl. How about air circulation? Do you have an oscillating fan going in the room with the plants to move heat around and help with strong root growth? 

Okay, aside from those areas. In the future, best practices for seedings recommends using a soilless mix for germination. As an example, one of my master gardeners uses coco coir and distilled water for their seed germination trays and then transplants into a good potting mix once they have 2-3 sets of true leaves. She recommends General Hydroponics Advanced Nutrient System Flora Series as a fertilizer for later because it can be used in hydro/soil/coco mediums and supplies all the NPK needs of the plants during various stages of growth. There is a chart on each bottle for a: cuttings and seedlings; b: general purpose - mild vegetation; c: aggressive veg growth; d: transition to bloom; e: blooming and ripening.

You don't have to get that fancy though, there are definitely plenty of good soilless options out there to purchase and a little goes a long way in small seedling trays. Also, seedlings don't require fertilization so I wouldn't start out with any fertilizer present in the future and only add as your plants develop. This is the last likely problem I mentioned earlier. If your soil has too much nitrogen in it, you may end up with leaf curl as well. Some potting soils have fertilizer added in or just high amounts of NPK. Try the soilless option next time, keep a close eye on watering and light, fingers crossed, and hopefully your tomatoes will flourish. 

Thank you for contacting Extension and please reach out with any questions in the future.