This paragraph are copied from their web:
You can't overdose* the NP Reducing BioPellets. Once your filtersystem is working optimal, the number of bacteria fluctuate according to the availability of nitates and phosphates. When the availability of nitrates and phosphates is low, the numbers of bacteria will decrease. When more nitrates and phosphates come available due to eg. feeding the numbers of bacteria will increase again as you can see in the example below.
So it's still safe even if u add too much pellets.