Sick plants. I need a DOC ASAP!

My plants are having some yellowing leaves and some brown patches form on the leaves. Mainly on the leaves at the bottom. How do you add only N to a hydro reservior? These problems are killin me plz someone help!

just add a nute that is very high in N and low in other stuff.

brown rust colored spots? Are you using cal/mag?

I wouldnt feed any N just yet if it has brown rusty patches, could be a number of things including OVERDOSE !

I don't think it is an overdose. The ppm are pretty low and I have been slowly bringing then up. I am not using cal/mag....should I? When you are adding nutes, do you add exactly the ratio that they say on the bottle or do you use half strength? Some of the leaves look like they have been bent at a funny angle. they are still rightside up but just bent about 80 degrees. one of the other plants has light yellow spots like some kind of camo all the way up it and the bottom leaves are yellow.

that sounds like it could be more than just one thing... need pics bruh