It’s correctable BTW … clip off the most necrotic leaf. It’s not nute burn , it’s riding up the serrated edges instead of full leaf necrosis.
K def.… You can easily adjust this by adding seaweed / kelp …. Easy to mix up in a gallon of water. I use a capful in a gallon of TAP - NO PH NEEDED.
Seaweed contains several useful plant nutrients, including nitrogen, potassium, phosphate and magnesium. There are dried and liquidised forms available from garden centres and seaweed is a common additive to fertilisers, both organic and non-organic.
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I would ride out your last feed ( let plant burn thru it ) then simplify your feeding. No need to flush as that would unbalance that medium even more.
Simple watering as needed ( with kelp ) then water to burn thru Gaia until you need to re-feed or top dressing more FFOF. ( which is even simpler. )