When I bought my 55g used the guy gave me a bottle of that stuff with it. I used it, following the instructions on the label, and I never had a true cycle, but there are also many reasons that this happened. I would assume that because the LR was in the tank (along with the LS) for two years prior to my buying, that probably skewed my results. I am sure that there was probably a good amount of de-nitrifying bacteria already established in the tank, so my results are kind of invalid. I cannot say that it does work for sure (because of the amount of variables) but I cannot disprove it either. I would say, if you already have it, use it because it will just add to your bacteria and wont harm anything.