My pills were 400mg each. It has been suggested 400mg/100L. Someone else said 250mg/100L. I seem to remember using 4 pills in my 280L tank which was probably overkill but I didn’t know the dosage at that point and it certainly worked without harming the filters or fish.
I dissolved them in a cup of water first as they have a white coating which takes ages to dissolve.
I siphoned out the dead cyano quickly (it starts to die within 24hrs) then repeated the dose 3 days later.
Someone else asked and I suggested 2 pills for his 280L tank with a repeat, as above, 3 days later and he reported back that it worked well.