sick plant.. magnesium def?

flushing wont hurt! plus it could deal with a nitrogen lock up due to a PH issue, and if thats the case adding nitrogen wouldnt be good
on secound thought I would if it was me I would flush then go to 1/2 your nute mix and wait to see good green growth. those new
pics got me thinking adding might be a mistake

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You use BioBizz,so its Cal or Mg def.
I'm using Biobizz since 2002 now and I always had problems with Mg/Ca. Though, your tap water pH is 7.5, so might not need to add calcium. Lockup is pretty uncommon because BioBizz products are made for lightly alkaline water. Most of their products lower pH.

So I'd try some Mg/Ca chelate and hope for the best. BTW, one of my plants had a similar deficiency 3 weeks ago. I fixed it with some tap water + epsom salts diluted.

Cheers!