It's not 'full hydro'...in hydro, the roots are constantly in a nutrient filled solution, whereas in perlite, which actually holds very little water and no cec, they are not. it's not exactly the same thing!Precisely you must have a TDS or EC meter. You are full hydro your substrate does not buffer you so your feeding must be within a smaller window of acceptable.
Looks to me like you have both a Ca and a Mg deficiency. Up your Ca and Mg supplementation for now. Get that meter. I've had great luck with this one
https://www.ebay.com/itm/HM-Digital-TDS-EZ-PPM-Meter-Home-Drinking-Tap-Water-Quality-Purity-Test-Tester/371498703640?epid=1600169615&hash=item567f0c5b18:g:1scAAMXQS6pRvc2x:rk:1:pf:0
Perlite is full hydro.