Ya, i agree with M0use, if they are yellow like that with a 0.4 EC, shit thats like 400ppm man your ppm should be 3x that at this stage. I initially thought toxic soil, but revealing that EC, shit man feed the girls! 1200ppm! If i were you, i would give the plant a solid flush with a 6.2 pH. Have at LEAST a gallon runoff out the bottom. Try to use room temp water over cold because some salts won't dissolve in cold water. Then put the plant back and allow for the soil to dry a bit so the pot feels light to pick up. Then you water in a 1000ppm solution with a 6.2 pH
I wouldn't suggest you go from 400 ppm to 1200ppm in an instant. You'll likely burn them. try even 800ppm to 1000ppm and see how that goes.