Was it 99.99% aloe vera? And how much did you put on and how many times?
I put 99.99% organic aloe vera on my horses rubbed tail twice and day rather generously. I also wash it in johnsons baby shampoo a couple times of week.
is it actually sweet itch or is he only itching his tail?
I might regret saying this, but I think I've got my sweet itch pone under control! Combination of a sweet itch rug, homeopathic tablets once a day, cider vinegar once a day and neem oil on his face and ears. I tried Global Herbs Skratch, which was recommended, but it didn't work at all for him.
I've come to the conclusion it's really a case of trial and error as what works for one doesn't necessarily work for another. So you've just got to hit on the right combination of things for your horse.