Are you circulating the air near the plants? Take a thermometer and put it on channel next to the plant; if it's above 90-95F there, you're running too hot. Plants look heat-stressed.

Get a fan that makes a good breeze and blow in the space between lights and plants.

Nutrient temp is too high to contain much dissolved oxygen.

Thanks for the reply. I have moved the lights up, turned up the fan. Also working on getting the nutrient lower temp. Will have to get a chiller most likely, right now icing down the soluton with ice bags.
Is there a max distance for these lights? I dont know if I can be 1 foot or 3 foot away for proper effect.

Again appreciate the help.

They look like t5 or t8 lamps and they are really all right at 6" minimum from the plants. HID lamps run hotter and have top be farther away.

For cooling nurtient solutions or even worm bins, here is the idea I've heard works well. Frozen water bottles. Put a frozen one in the tank and the other in the freezer and rotate each day. Choose the size of the bottle based on how much cooling or size of the tank. A very large (like 1 or 2 gallon bottle will probably require more than a day to re-freeze so you many need more than two if you have to go that big.

sounds like your ppm is a little high or such young plants... i would flush the roots with plain water and then lower ppm concentration. plants are so easy to burn but in hydro systems it is rare to under-feed but very easy to over-feed. just remember you can always add more nutrients if you underfeed but you can never take them out when you overfeed.

yellowing leaves is usually a condition caused by Nitrogen, either to much or not enough. what happens is the plants get a salt build-up in the root system and stop taking in the nutrients... in this case (nitrogen). once the roots are flushed of these salt buildups, the plants will return to normal growth.