Hello
so as you know nutrients are either mobile or immobile. the deficiency starts at the top or bottom .
in this case top . if you are running that low of a ec then it very well could be deficiency. in soiless medium an ec of 1200 microsemeins, maybe down to 800 Us ( micfrosemeins )for younger plants . what is the light level? lots of talk about PAR buts that is light color or spectrum but footcandles is intensity . foot candles should be in the 1500 to 2000 FC for seedlimgs/young plants. ( par is like ph/ec footcandles is the volume/filling rate of that par)
you could have just spilt water on it too .light/salt burn resulting)
a previous member wrote about the 20% over flow...that is the best advice you were given as far as the EC of your medium . it should never be more than 50% higher than feed solution ec. if feedbis 800 then runoff should be 1000 to 1200 .
you tell the medium EC by watching 4hr runoff which is why you do the 10 to 20 % over flow . if waste ec ever hjts 2 x the f3ed th4 plants are most likely suffering from nutrient lockup.
its important to make sure you have a complete feed solution with all 12 minimum required nutrients. N P K Ca Mg S Fe Mn B Z Cu and Mo
there is a lot of emphasizing cal mag...I do not know why this is ..cal and mag carbonate make up 70 to 80% of water EC as calcium and magnesium carbonate. it rarley is missing ever. any normal complete solution should have this .I line master blend for that reason. they just list nutrients....as any normal fertilizer does that is NOT made for weed .weed is. nothing special. it's a standard agricultural crop like corn tomatoes or Tobacco. only when it comes to weed do 4he ingredients disappear off the bottles like it's a secret.lol
any way when it comes to a deficiency or toxicity there is only on solution. flush medium with new complete 12 mineral solution at 1/2 strength either 1 to 2 plant pot volume. normally until EC drops 4o 25% to 50% above feed strength. it seems like they are a bit small for ec problems yet . 6ou can over feed for a while before nutrient lockup can occur but by then the ec will be very high. if you see it it is already too late . in veg it's not too big a deal as you can extend veg time. in flowering it is much more of a big deal as you lose a portion of the predetermined phases .
I could not recomend this book more .this covers evey aspect and in easy to read great detail. explains nutrients in great detail where you will know exactly what is in the formulas and how to calculate . all water , nft,sand, soiless', aeroponic, hanging drip feed virticle etc..everything
Hydroponic food production by Dr Howard M Resh
good luck!