Sure looks like nute burn to me.

Sounds like you have WAAAAAY too many ferts in there for your plants. Your testers says you have "plenty" Exactly how much is "plenty?" Maybe your idea of plenty and your plant's idea .......you see where I'm going with this?

You need to flush with ph correct water (6.2-6.8) usually 3-5 x size of pot (1 gallon pot....flush with 3-5 gallons of water.) Then make sure the soil runoff water coming out the bottom is the correct ph and give a final ph correct flush with 1/4 strength nutes..