Old topic but wanted to share my input. I'm growing hydroponic tomatoes (various strains) at university in a lab setting (indoors under HID lights) and outdoors in a greenhouse. In one of my greenhouse NFT systems, i recently had a similar problem on 1 tomato plant (total 9 plants that share the same res and tubes). But im gonna try to diagnose your issue by mentioning what others missed out on. 1 major cause of leaf curl is compaction of root system (i.e. roots are compressed or dont have enough space to expand). This risk is exacerbated in hydroponic systems that use tubes. This was the problem i had and had to replace tubes with square tubings that have a liftable top. Once you have access to roots, you must seperate them strand by strand (i.e. so they arent sticking together). In your setup, this risk will further be exacerbated because you filled the entire pvc tube with hydroton (right?). Remove hydroton from tube and place the plant in a net cup with hydroton. Nitrogen burns usually cause browning/yellowing of leaves (similar to sun/heat burn) and not purpling. Test your solution for each chemical if possible, or use a commonly employed aggregated measuring device that shows total concentration in ppm (dont let it exceed 2500). In my system, only one plant was affected. Coincidentally, it was the largest of all plants with the most root mass. I let another normal one grow to its size to see whether it would undergo the same problem, and it did. Viral and bacterial infections that cause leaf roll usually cause it to roll up. Same with the physiological roll. If your leafs roll down AND if your stems bend, this is caused by a diminishing turgor pressure (read: not enough water reaching afflicted area). Mist several times when lights are off (no photosysnthesis) and observe increasing turgor pressure (unbending). Or, untangle roots and remove hydroton from from pipes. I tested various growing methods including fully and partially submerged roots. They all work but a submerged root cannot intake oxygen; it has to borrow oxygen from another part of the plant (i.e. a root part that isnt submerged or above ground stem). This requires energy for transportion and isnt the most efficient (optimal) way for growth and cellular processes. Lastly, an airstone in the reservoir is useless unless the reservoir is completely airtight all the way up to the plant holes. Better to keep small airstones in the pipes right under the plant roots. Those that say aerating the res prevents bacterial development.. is false. If you dont have air in res, you will get anaerobic bacteria (they grow/accumulate slowly but acidify the solution); if you have air in res, you get aerobic bacteria (not acidifying but grow extremely fast). Most bacteria prefer aerobic environments for optimum growth.

I think it has to do with the variety of tomato and nothing to be concerned about. I have 2 "patio" tomatoes in my ebb and flow along with some indeterminates and they both look like this. I was worried at first that my nutrients might be too concentrated, but didnt see this on the other varieties and left them alone. They still grow like this, but show no other signs of poor health and are growing tomatoes just fine.

My four cherokee purple plants came from tomatoes I grew last summer, that came from a tomato I ate in NC the summer before. Last year I had a huge yield from 4 plants. This year, all 4 plants have been stricken with leaves curling up, new and larger leaves. Leathery, really curly little leaves and curled (up) larger leaves. Some small brown spots on larger, older leaves, no yellowing, no dead edges. Growing conditions are ditto to last year. Plants leaves are stunted, growth is stunted. You can see through the plants and overall, the leaves are small yep, and curled. I was told to use Happy Frog fertilizer due to calcium shortage. I don't think this will work. I am going to spray for fungus AND insects. These tomatoes are the best I ever ate, and I've eaten a lot of them. No more seeds available. I should have saved a few.

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