what causes the leaves to become discolored?

this is early stages of pottasium issues.. Proceed accordingly.

GFP

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Pot up, put plant in a bigger pot

with 20% perlite and quality soil

no nutes for 2-3 weeks

water well

good luck

 

How long have they been in the cups? I would up pot them into new soil...

 

follow steps one and 2 and then WAIT it should stop immediately and not spread...once you know your back on track then go to step 3.

FYI your plant looks good ...by the way no need for drastic measures. but a flush will line up the cation ratio and get you back on track.

GFP

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the main cause for leaves to discolor is improper watering. if you water too much or too frequent, you can overdose it with nutes, change PH, lockout other nutes, and worst of all, introduce pests, which can then give you diseases. then sometimes when these diseases show up in form of deficiencies, people throw in more nutes, and then it just makes everything worse. it sorta happens in that order too. "deficiencies" are pretty rare in soil like in what youre growing (i wanna say thats soil lol).

in your situation it almost looks like drops jumped out of whatever you were using to water and spilled a bit onto the leaves, dripping down to the tips where it chilled and burned the leaf for a bit. just a possibility since its not everywhere else on your healthy looking plant(apart from those tips). also looks like it grew out of it afterwards. i honestly wouldnt flush. just be patient and let some air do the work for you. check your runoff ph and ppm to make sure theyre in check. if theyre insane then flush but I have a feeling youre good judging by rest. also wouldnt hurt to inspect the rootball for root aphids and to see if its rootbound as both of those will also cause similar symtoms that would only be made worse with flush/extranutes