need more info. What and how often are you feeding? What light and distance? PH runoff?

Looks like overfeeding and or over watering or both, i am assuming you are growing autos bc there notoriously eays to burn, flush out your plant check ph, prune of the really burned leaves as they will not recover this will improve airflow, with autos u go with half the recommended dose and sometimes even this is to much, in veg i use botanacare pro grow fish mulch and nitro mostly and never burned an auto in veg, i use ffof people think this is a hot mix it is not it is just chocked full of nutrients, with autos the number 1 problem is overfeeding, you need to wrap your mind around how little nutrients thes autos need, for flower and cant recommend enough Atami Bloombastic but u must go real easy. Pics are my last grow of 2 critical plants and 1 toof decay autoflowers. Need more help ask.

I am using a mix of happy frog or fox farms original mix for soil and their trio of Nutrients (grow big,big bloom, havnt used tiger yet) and also cal-mag I have only gave them nutrients twice. I water them about every 3 days or so, PH in the soil is 6.5~(DONT know if meter is accurate) and I don’t have a meter to meter run off (waiting for it get here ) and honestly I don’t really know what the seeds are got them from a buddy all he knew is that they were some type of lemon strain. Can I flush the plants ? If so about how much water they are in 3 gallon smart pots. The light is about 12 inches away the light I’m using is a mars hydro Ts-1000 and figured I would mention only 2 of the 4 have this problem