runoff imho is useless info, for it to have any meaning it has to be collected without cross contamination from trays, and even than we just have to accept a higher EC in the media than what goes in chemical form, and normally also a lower PH than what goes in, chemical ferts are mainly acidic, so over time it will acidify the media to some extent, if you have a runoff of 20-30% (drain to waste!!!), very rarely you will see toxic salt buildup, given the plants are healthy and "eating" tho.
just see if the problem with that phenotype stop or not.. nothing much you can do at this time, the problem is already there and the "damage" already done, you will have to find why it happened if you choose to keep that pheno. Too much K ?Too Much mg? PH range of the media & feeds ? etc etc etc
This is dialing in phenotype growing, some are finick some not. like @HerbalEdu said.