Well from checking the International Cannagraphic Magazine Forums - The Complete guide to Sick Plants,pH, and Pest troubles! & watching the colour of the WHite KC seedlings it looks to me now that instead of an overdose of nutes there all suffering from nute defiiciency after being flushed.

Have watered all the soil plants with a .75 ml nutes .45 ml of Superthrive per 2 litre litres. The nute are advised at 2 ml per ltr so thats just under 25% strength & the ST works out about 90%.

Will see how it goes & post a weekly update of pics at the end of the week.