You have salt build. The shape and colour of are obvious tell tale signs that this is the case. If you think you know better and you don't fix things it will get worse.
I've seen this before in my own grows and there's only one way to fix it. Do a big plain water flush, about 50 litres per pot. Get the ec down to about 0.8. Then feed at half the dose about 0.8 ec and pH of 6 for a week. Then go to about 1.4 for the rest of the grow.
The plants have enough nutrients stored in the roots. There's no danger in flushing and reducing EC in.