Please help me plant emergency!!!!! I have no idea whats wrong

my plants have shown brown tips and curled under leaves for quite some time now but just in the past few days the problem has gotten SIGNIFICANTLY WORSE and im afraid of LOSING MY PLANTS!!!! at first i thougt it was nitro tox but im using mg soil and ive only fed my 2 month old clones once . could this be overwatering, could this be ph problems, i am flat broke until payday so i need a fast free solution!! please forum vets save my plants!! OH i forgot to add that i may have overused superthrive and im using drinking water because that was all they had at the pharm, could the minerals in the bottled water be doing the damage? here are some pics

dude im telling u miracle gro,kudzu compost,and either FIMming or training ur plants are the best way to do things!

so that does nothing to answer my question whats going on here?

This is common from MG soils...They do well at first then sometime in the middle of the grow they seem to burn the plants....I noticed MG does well out doors...what i thin it is is the soil has a lot of slow release nutes, that over time they build up through slow realease, eventually suffocating, burning your plant and making the soil toxic to it....thats just my theory...i dont touch MG at all...i use DR. Earth and composted soil....and i never had this in any of my crops... that only time i had this was when i burnt my plants giving them too much guano tea, and it was never near as devestating as this....if i were u, repot ur plant into some good natural non fertilized soil

Holly fuck is that the main stem thats brown like that? Baby is goner if it is...TRANSPOT immediatly, but i think its too late, i never seen a brown stem like that

Its hard to say whats going on here do you have a soil ph meter? do you have a soil moisture meter? If I were you I'd borrow these things if you havn't got them and find out whats going on bro could be many things defs, hotspots in the soil if it wasnt sifted or mixed right. If you have this equipment at least you can rule out the obvious things!

looks fucked to me, maybe too much water or nute burn