test pH? maybe that rez has soemthign growing in it?
what is EC? if above 1.3-1.5, try lowering.
is it possible you mis-measured soemthing? i once mixed up a couple gallons for a water tank, but i accidentally did 1gal worth of nutes... after a coupel irrigations i saw the effects, lol.. oops, thankfully it was on light side and not a double dose.