First off don’t fret you won’t lose your plants. That looks like calcium deficiency to me. Now that is one that happens to lots of people who use cleaned up water. Many city water sources simply don’t have it. If you filter you water as many do or buy purified water then you need to be adding it. I run off a well so my water has plenty. Any grow store will have a bottle of CalMag and get the cheapest stuff as it is all the same. It is a common thing needing to be added to city water.
Now on the nutes issue... there are two kinds of nutes, macro and micro. Calcium is a micro. It is kind of hard to overdo micro nutes as the plant doesn’t use much and doesn’t absorb much. But the real reason you read to be careful is adding too many macro nutes is will cause an auto to start flowering early. Then you get a short plant with low yield.
You have a very common problem. The plant will recover fine. But the leaves with that discoloring will never heal. Once that damage is done it is permanent so don’t look to them and expect any improvement there. But by adding some cal mag you can stop it continuing.
Good luck!
