So in three years your peristaltic tubing has not needed to be changed? That stuff erodes quickly. I get 6 months or so out of a 5 lb VO2 tank. If I had a 10 lb one, I could go a year on my 250g of water. That is about 5x the size of what you are dosing for. I have not yet needed to refill my media yet, but I suspect I will get at least 6 months if not 8-9 out of a single container of ARM. edit, I don't want to sound condescending about the 55g to a 200+ g tank, but you would go through 2(3) part supplies 5x faster with a tank of that size.