Yah you're right, unfortunately i've yet to see bioballs with rough surfaces. So far i've seen one brand of bioballs that comes with a bio-sponge in the centre of the bioball which to me is much better as compared to the normal ones.
Smooth surfaces can also have BBs BUT it can't colonise as many BBs as rough surfaces eg. if you were to compare CR to Bio-sponge, you'll need to use very much more amount of bio-sponges to colonise the same amount of BBs as compared to CR medias. Which means you're not making efficient use of whatever limited spaces you have in your cannister or overflow filter.
As for replacing old filter medias.... If the media is clogged up internally, it is deemed not as effective as when new. Meaning the total surface area (internal and external) that is stated on the packaging of the media is now lesser due to the clog, thats why manufacturers recommends that consumers replace them regularly to maintain at optimum level all the time. But if you're kiasu like alot of us including myself, who pack our filters with as much good biomedias as possible, we may actually have more than enough medias to provide enough external surface area for the BBs to not bother about the clogged up internal parts of the media. Which means we actually don't need to change the medias.
For easy comparisons of the different types/brands of biomedias, let us use m2 or sq ft since most manufacturers use these 2 units of measurements.
From the converter calculator,
273,000mm2 of surface area = 0.273m2 = 2.9385sq ft
As compared to Eheim Sub Pro's 450sqm = 4,844sq ft of surface area.
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