I got the Bactinettes which was refrigerated from my LFS, I have an unknown filter with just supplied with the tank, just basic filter with no carbon, I made a hole at the top of the filter sponge and poured the Bacinettes into the filter sponge, to stop the Basinettes coming out I put some cotton wool to cover the hole which I made. Put a dead prawn in the water, Got some water from the tap, added Tetra Aqua Safe, done a test in 1 day with API Water Kit, had low ammonia, nitrite reading, removed prawn, day 2 test ammonia 0 nitrite was 0.25, done a 20% water change added x4 Fry Fish, checked water in a week and conditions ammonia and nitrite 0, 2 months later the tank is still going strong and hasn’t lost a fish, I bought this for my hospital tank but most of the time I just keep fry in there until there big enough to go to my LFS. If I have an ammonia or nitrite spike I will certainly be using it again.