From what I can tell, most reactors are the same. Octopus does however make a Bio-Pellet specific reactor that from all appearances is really nice. I think the recommended amount of pellets for my tank was 750ml. I started at 500ml after reading stories that it is best to start slow and work up. I did contact Jon Warner, and he told me not to run more than 500ml in my system, and to actually go out and buy more fish. So the amount really depends on the bio-load, not the tank size. Brian, if you are thinking about running them on your 75 I would start with the small jar of 250ml in the reactor. Another thing I have discovered is you will not need to run carbon, or GFO while the pellets are going.