I have had success with this method, with only 1 fish dying. I hope this will help
But please note, I started treatment at the first sign of ick, one fish had 2 spots. The next day all fish were infected, with 2 fish completely covered in ick...one died...one survived. I am in my 6th day of treatment and all are doing well with no signs of ick.
I recently bought 10 black neon tetras and have them in my quarantine tank. Of course they became infected with ick. I have my temp at 82 degrees (I think 89 is a little to high, you could be stressing the fish more)
After 3 days you should notice most fish free of ick.
I also do a 80% water change every day, making sure to suction my bottom gravel to reduce more ick. I also rinse out my filter.
Of course I may be deleting most of the good bacteria also, but I am choosing the lesser of evils.
I also over feed the fish (flakes and blood worms) to ensure their health.
( remember I am changing the water everyday, so the excess food is also being removed
The life cycle of ick at 80 degrees is around 3 days. What you are treating is the free swimming ick (reducing their numbers). Once they are attached to the fish that is it, meaning the damage has been done and the ick will remove itself when it has finished feeding on the fish.