There are two important variables that I think people need to consider here when evauluating whether the pellets are effective.
First, the flow through the reactor. I was corresponding today with Jon who shared an interesting story with me concerning a tank he maintains using ecobak. The client had an inadequate skimmer and high flow through the pellets. The client had about 50 nitrate and 1.0 phosphate The client had a major bacterial bloom that caused some problems with the system. However, in less than a 1 week period the client brought his phosphate and nitrate down to nearly 0. Jon seemed to indicate that the high flow was the culprit which caused this major bacterial bloom and rapid and sharp drop in nitrate and phosphate. Now, although inadequate, the skimmer apparently seemed to me to be doing an adequate enough job because the nitrate and phosphate had to go somewhere which only leaves the skimmer as the means of export. Therefore, it appears to me that the sharp and rapid drop of nitrate and phosphate was directly related to the high flow through the reactor. As such, if you are not seeing enough drop in nitrate and phosphate, I suggest gradually increasing the flow in the reactor and see if things change. I would suggest to up the flow in the reactor in small increments and leave it alone for several days and test your levels to see if it is helping so as to avoid a major bacterial bloom.
Second, the appropriate amount of pellets to use on a given system is still very unclear and will vary wildly depending on the particular stocking, feeding, and water change practices of the individual tank. Therefore, adding more pellets seems to me to be also necessary sometimes when you are not noticing a drop in nitrate and phosphate. As long as done gradually, I do not think you can overdose because the bacterial colonies should be limited by other finite and necessary resources available in the system. But I may be wrong about this, although that is my understanding. If correct, this could be the answer for many finding the pellets ineffective.