I think the buse nutrients is not enought for they i was use 1,1 ml/L and plus the max sterngh od addictives.
if it's a deficiency I don't know exactly which ... could be Magnesium.
to SAFELY AND QUICKLY find out if it's Magnesium get Epsom Salts from the supermarket (it's Magnesium Sulphate) spray leaves with 1.25 grammes of salt dissolved in 1 litre of water. if it's a Mg deficiency the leaves will go green again within 24 hrs. if does not fix will not hurt your plants.
The brown spots dont grow since the flush but the leafe curles is stagned.