Deficiency

your plants are looking pretty good. Normally when its yellow on the tips and edges then tuning brown its a sign it wants more potassium. and when it gets a dark green with blue hue its a sign its over fed with Nitrogen, this tends to be accompanied by tips of the leaves clawing down. The smaller plant in the top right corner could use a bit more K, that's what it looks like to me with out going into it. But be careful if the EC is to high adding more nutrients will not fix the problem just make it worse. growdiaries.com/journal/what-is-electric-conductivity-ec-and-total-dissolved-solids-tds Good Luck!