Believed Potassium Deficiency

I am growing in soilless using pura vida 2 step aggressive formula. 2 days ago I noticed yellowing on the edges of some fan leaves. The leaves have also been curling for some time. I then thought it was a Potassium Deficiency. I bought Diamond black and watered them yesterday. Today I wake up to find little has changed. Do I need to give more time and potassium rich feedings, or should it have been cured after one feed? Could it be another deficiency or lockout?Thank you
 
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