little tacoing and rust spots...
EC of 3's and 4's? really? this is too high if true.. probably lockout. But, i'd expect to see a bunch of coinciding symptoms if this were true. I guess if it's every 3rd irrigation it's protentially okay? would need more info to rule that out (rhetorical) -- you have that info so if you feed that much more often, it is a possibility.
The rust spots on their own are likely Calcium related. BUT, if EC is really that high, lockout is possible.. high p or k coud cause this but you'd also see other issues on the plant concurrently.
Manganese toxicity is another possiblity of the rust spots. Check labels of what you provide.. if something is high in this, you don'tneed much... talking millimoles per liter.. 1/100th to 1/1000th of the primary nute concentration levels. ('millimole' is 10^-3 of a mole so "6.023*10^20" instead of 10^23 .. numbers so large it's hard to fathom)
the "taco" curling can be from heat or light in most cases.