Yup. Looks like nutrient burn, plus there's no perlite in the soil.

Double check application rate and frequency. a 20-20-20 fertilizer, at best, is an every other week strength. (or 1/2 strength, once a week) It's not a time release nutrient, is it?

Get some perlite or a potting mix that has perlite. It aerates the soil (lightens it up) and prevents soil compaction. Otherwise, you can end up with a muddy mess that suffocates the roots. Too late to add it now, but on your nest transplant...or future grows...your plants will appreciate the addition.