Plant wilting

Possibly lower (winter) temperatures causing your plants to have a slower metabolism, therefore a lesser need for nutrients, leading to what looks like nitrogen toxicity. Try going to plain water for a few days and changing to half strength nutrients once feeding resumes. Can't be any worse than it is now, and will eliminate or prove one theory as to what is occurring, but I do think it is a slower metabolism due to the lower than average temps that is the cause of this. The fact it is happening at the same time of year, each year, would support my hunch. Hope this helps,......... Organoman.