I think it was simply just a stability issue in the root zone between water, nutrient concentration (as the media dries and plants uptake water nutrients can become more concentrated), nutrient ratios (same deal without frequent feeding and run off)
, ph fluctuations in the media etc.
Ok, thanks. It's weird that it's just popped back up again even though I am watering more frequently now, and it seems worse as I lower the feed ec, hence what made me think it's a deficiency. Hopefully if I keep up the daily watering it'll stop.