I'm probably the wrong person to answer your question about Sterazin as I am totally biased, I think it's useless. However, I have breeding friends that love the stuff. You will find that the dosages have changed depending on when you bought it. My last bottle was "double strength" and from England so the dosage was different again. My biggest problem with Waterlife is that they never mention the ingredients on the bottle which IMO should be outlawed and if you are running thousands of litres of water it is 5 times the price of other products. For me, regardless of the dosage, it simply did not work. These days I use my vet and not commercial products. The advice you get is generally better than your LFS and the meds work.
MAC