Question:
The Claris water filter is designed to remove 75% of the carbon hardness,

what is carbon hardness?

Answer: Various molds & algae might be delighted with the "organic material" of the filter as a habitat, submerged or not. Which, of course, applies to all in-line filters equally, and argues for regular replacement of cartridges. I'd also advise taking a peek & a swipe at plastic surfaces usid in the housing of same.

Wayne- any knowledge of the specific mechanism employed for reducing limescale buildup, & how many gallons a filter like this softens? This is important, because in Brita pitchers, eg, the softening action may not last as long as the other functions of the filter.

Many in this group would/should be ready to consider softening. Anyone with a heat-exchanger should think about it- tests I've done on mine show that plenty o' Ca may go in, yet precious little comes out. (to wit: Pur-filtered input reads 120ppm/7gpg, 'distilled' condensate at the wand reads 0-25ppm/0-1.5gpg.)