Tomato Lower Leaves Yellowing

[Izzie1701]

I am having some troubles with my hydroponic tomatoes. This is my first time growing. My bottom leaves are turning yellow and don't look healthy. I have planted all my tomatoes from seeds. The plants I planted in the ground are growing twice as fast as the plants hydroponically and look a lot healthier. From everything I have read it appeared I had a lack of nutrients. I purchased a TDS meter yesterday and tested the water. It was at 2200ppm. I thought this may have been high and was due for a nutrient change so swamped the nutrient out and adjusted to 1300ppm as it indicated it should be at on the nutrient bottle. I am using a 2 part nutrient with a third boost nutrient. From further readings it looks like tomatoes should be fine with a nutrient level of 2200ppm. I am running a dwc system. I have my tomatoes in rockwool surrounded by clay pellets. I have about 1" of the bottom of the rockwool sitting in the water as the roots are yet to protrude through the rockwool and dangle into the water. I have a 6" air stone in a 5 gallon bucket supplied by an aquarium pump for aquariums up to 80 gallons. I would hope this is enough air. Any idea on what the issues could be. The leaves are just yellow no droop or curl up.