Hi Finn!
Again, I am nooooo expert, I'm always asking similar questions!
What I will say to you though is that I just went through the same thing, after introducing some new plants without quarentining them

All my babies, that I've had for over 4 years from tiny little things, got sick. I also used Protozin, but after being wrongly advised by my local pet shop as to the size of the tank, I overdosed with the med. I killed all but 2 of my fish.
Basically, what I am saying is, this stuff is probably great at what it's supposed to do, but please please don't put any more in than you are supposed to. Also, check, double check and triple check your tank size and calculations before using it more.
Feel free to post your tank measurements here, and I / others will tell you what you need to know.
I really really hope your fish get through this, and it's great news o hear that the ick seems to be decreasing.
Keep us posted, there are some really great people on this site.
Good luck!