We have not had our Fine Pond Filter Pad tested for a micron rating. Some of our aquarium pads have been tested since these pads are able to polish the water without the pads clogging up to quickly. In an outside pond there is potential for a lot of debri in the water. We have tested many pond filter pads and our fine pad has given our customers the best results without clogging up too fast while producing crystal clear ponds.