Clones not doing well

Hi, I have sprayed with cal mag the past two nights, no dramatic improvement but no worse. Would you recommend the Epsom salts in addition?
If so could that be added to the res, and what ratio?

Tonight is a feeding night and I have been doing a (20) gallon res with my standard mix of nutrients to feed all (70) cuts, (23) of which are not doing well

Thanks!