what quick fixes could I try
Foliar feeding is a possibility. It will help with the deficiency but unless you correct the root cause (pun intended) the deficiency will just come back worse. You are growing in small containers so the plant is going to use those nutrients up quickly and you’ll need to replace them frequently in small pots.
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Those plants need potting up into bigger pots and given a good water/feed. They'll perk up soon enough. As Monkeydo said you'll have to increase the fertigation more frequently in those small pots.
Good luck
The plant is in a competition in the 40oz cup competition but I think I might just make it the other one I have be in the competition to try and fix this one thanks for the idea. I wasn’t originally gonna move it up at all. (In the competition we can only have one plant after 11/1 so perfect timing.)

Ah ok..sorry I didn't realise it was like a solo cup grow. In that case increase the frequency of feeding and maybe try a foliar feed. The plants gonna use up the nutes real quick. Treat it like a hydro/Coco grow
screw the competition lol, thanks for making my brain work because I actually remembered my garden isn’t under regulation 😅
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