Another photo of two SURF2 or 2x or 2xx scrubbers from the UK customer above. Here you can see the white edges of the Green Grabber rock surfaces are much more covered in growth, which is the normal process because algae eventually covers all rough surfaces that have the proper light and air/water interface turbulence.

Of more importance here, is the fact that there are two scrubbers instead of one. Two smaller scrubbers is always preferred over one larger one, because scrubbers actually remove nutrients from the water, but do so mostly when they are growing thick hair or thick slime algae. When you clean a scrubber all the way down to the white reflective surfaces, you don't have any more thick growth for a few days, and you will see the difference in how long your display glass stays clean and other ways. So by having a second scrubber that you clean on alternating schedules (one every 5 days, for example), you always have the other one growing thick and filtering.

Other aquarium filters, however, such as protein skimmers, filter socks, etc, don't remove any nutrients at all, and thus it doesn't matter if you only have one of them because cleaning it won't change anything.

Click image for larger version

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