What do U think is wrong with these plants?

A Master Kush and a Chupacabra. Both in 5 gallon.DWC, 1/2 strength GH Flora series. Week 8.
Started from seed, then put the sprout in Rockwool cube, once the roots came out the bottom of the cube I put them in DWC. Gave them 1/4 nutes for 4 weeks, then went to 1/2 thinking this was a nutrient deficiency problem. PH at 5.5 to 6.5 water temp 80f. TDS reads about 450 on both. Theres only slight amount of algae. Under high quality LED lights, good ventilation, no bugs.

The bottom leaves have always been yellow and the growth is slow. The Master Kush only 4" tall after 7 weeks. The Chupacabra is about 6" after 7 weeks. They are starting to droop now. Is it Cal-mag problem?

Any opinions will be appreciated but if you've seen or had this problem, I'd really appreciate some help.
thanks.

Gordon