My seedlings have some sort of deficiency. Please help!

Hope everyone is doing well. I'm hoping someone can help me out as I am a noob to growing.

So here's the problem. I am using rockwool as my grow medium and personally believe that I did not properly flush it before growing. I say this because, 1 I was not able to test the ph unfortunately, 2 because the plants that I had going g before this set grew a hell of a lot faster (sadly they died because I went out of town for 2 days and was unable to water them) Now I do have ph test strips so I can set the ph right. I flushed out the rockwool with water at 5.5, and now I'm watering my plants with a water at 6.5. Sadly the burns on the leaves are not getting any better. In fact from the start, 2 out of the 4 plants' first two leaves seemed to become brown and die very earlier on, though the plant still did grow. So take a look at the pictures and let me know what your thinking.

I do not believe it is because of heat and light that is causing the burning, because the last set of plants had no problems. Again I'm just a noob though. Can anyone help me out? Please ask questions if you have any. I really would like to learn.

They look better than mine,keep your ph at 5.8 when you have a problem first thing to check is ph. I would put them in what system I was running and wait. I been trying to find out what is causing my slow start and it may be that my expectations are to high.

nute burn back of with the nutes they only need about 50 ppms at this stage , and i guess you pre charged your rockwool too right ? not a def just a bit of nute burn therl be fine

Rockwool isn't very forgiving for a noob. For a noob it's hard to screw up Jiffy pellets. Then you can put them in a 4 inch rockwool cube. But, as you are finding out, you need to pre-soak the rockwool to get them ph stabilized, and be very careful with the nutes. good luck

Edit: I did not start adding nutes until yesterday. So at the time this picture was taken they had not been receiving nutes. 1 of the plants has become rather large while i have 1 medium sized one and the 2 others are stunted in growth. The largest plant's leaves began to become a lighter green yesterday as well. I don't know what is up with that. And one plant still has some white burns on it. Does not look like mold. I am getting different problems on each plant it seems like haha. Thank you again everyone!

Anyone else have anything more to add??? Any advice?

I need some help here. Anyone please