I'm using the 15-5-20 tap and had very good results with it both in soil and now in coco/perlite or coco/perlite/vermiculite.
I purchased it back in March or April and like you thought my plants hated it (the few that I tried it with at least during mid-veg *soil*). Turned out being a salt...
I'm currently in a grow with most plants using the Bruce Bugbee's peat/verm/lime/gypsum combo with the g-13 and Moby dick clones (1 seeded pheno of Moby that shot straight up/thick stalk..interesting because I finally got to see the more sativa dominant traits of this one..other Moby's are...
Did you try this (20-6-22)? Found a great deal locally @ 6 bucks for the 1.5 tub. I also noticed UB's post but that was for the professional line that's 20-3-19 + high nitrate vs Urea in the FeEd line of this product. Also the pro version has magnesium added.
Very good info on this topic. I also replied to another topic similar to this one on here.
Current set up -
**2×4 closet grow for veg running (1) 100 watt S1000 Bloomspect quantum board + (1) Unit Farm UF2000 100w QB
(will rotate in an additional 240w Yuanhui LM301B + 660nm Epistar reds...
I was also intrigued by this video as well as some of his others. I decided to give it a try as well. I agree! 30+ years research it's a no-brainer for me to at least give it a go! It's my 3rd grow and i wanted to try something different. I've got a couple of Moby Dick clones running the BB...