Your ec of 1.4 is that just fert ec or water and fert together ? Basically what's your water ec is it hard or soft water cus if its hard lets say 0.6 ec and your only giving 1.4ec total then yes your prolly under-ferting plants cus in reality that would only be 0.8 fert ec if you take away a hard water ec of 0.6. I hope that bit makes some sort of sense cus im shit getting point across at times.
No need to do the dipping of run off thing if its summink like the hard water scenario above, just up ferts as you planned originally.
On another note it may well be a fussy coont and it could possibly be summink like soggy rootage and if that's case maybe let it dry out 3 to 4 days.
TBH Wu im just giving you possible things it might be here cus it dont look that bad from here . Anyhow just a few things you could try out to get to bottom of the problem their mate is all.