LOL. 85% to 98% sounds confusing. Just say "I'll make it look a lot better!" I was frustrated too after my first attempt to remove those exact fert. stains. Here are the mistakes I made. 1. I didn't hit the concrete with enough pressure, because I was worried about etching/marking it. It was a white soft poorly poured slab. You have to surface clean the snot out of it first, really pound it. 2. No mist, make your tip pour it on. In the end, I used 2 cases on a 1,000 sq ft. driveway that was 50% stained. It took about 3 applications over each stain. It was easily a $800 job that I only bid at $200 bc I didn't realize how much chem. it would take. Nevertheless, it was a great job for practice and marketing.
This morning I used f9 to remove heavy iron stains off limestone siding. It worked like a champ! Now its just a matter of finding more customers who are willing to pay the premium for the chemical.