I've grown squash in 5" net pots inside a 6" pvc pipe and tomatoes, peppers and eggplant in the 10" net pots inside 3 gallon buckets. Both ran drip for a few minutes each hour, not constant like nft so I needed more medium. The net pots had grodan and clay pellets. For things in nft or water culture I would use much smaller since the roots grow out the net pot more. For drip and ebb and flow a little bigger is better to hold the moisture. The medium you use makes a big difference too, rock wool holds way more moisture than perlite or clay. There is no set guidelines I've seen but the plant will let you know if it needs a bigger pot.

Thanks Blue. I can now see you are 100% right - the 18 slice 2" mesh net pots came the other day. They weigh 4.0 grams each, too flexible, and the lips are tiny and molding shoddy. The only way to deal with them would be to buy a 1 7/8" hole saw. To add further insult, about 10% of the lips were not completely molded, i.e., missing material and are worthless. These disappointing mesh net pots came from hydroponicsnation in CO via eBay. They are obviously not reliable for most veggies, though they might be pretty good for Spiritweed, garden Dandelion varieties and the like. I may just snip the 16-slice bottoms out and insert them in the durable 4 slice bottoms I'm using currently when I get a chance. They came from homeandgardensupply in RI via Amazon, and weigh 4.5 grams, which made all the difference to their integrity and clearly superior durability and molding.

I'm going to guess you damaged the roots during transplant and they haven't recovered yet. Here's my rationale: turgidity occurs when transpiration is greater than absorbtion; since your plants are heavily shaded(or picture taken in the evening) its probably not so hot the plant is transpiring that much. The new leaves appear unaffected; root damage usually occurs to older roots as they're bigger and more likely to get broken and the younger roots are actively growing thus more likely to recover from any damage they receive. Of course it could be over watering is killing your roots thus yielding the same symptoms. you might try something more along the lines of 1/2 on, 4 hours off.

Net pots support the plant and allow plant roots to grow through the net so they can get oxygen. Net pots need to be big enough for the roots & strong enough to support the plant weight. The mesh of the net pot is also important a smaller mesh allows one to use media with small particles whereas a large mesh will need a media with larger particles. Net pot liners may be added, however, to contain the media. When placing pots in a system, they should sit ¼ of their depth in water. Home or cheaper versions of net pots include strawberry baskets, small fish nets, Styrofoam cups with slits on the bottom, or plastic cups with holes placed in them by a soldering iron, etc.