How does calblock (water softener) work? This "calblock" device claims to prevent limescale accumulation on water heaters in a washing machine. It sits between the water faucet and the washing machine; the water passes through it.
I cannot imagine how it could work. This video, made by a supplier, describes its function this way:

Thanks to 2 magnets, at a low temperature, molecules of calcium bicarbonate are splitted in aragonite, smaller molecules, that remains sospended, is not deposited and is discharged with the waste water

which is not satisfying at all.
How do the magnets convert calcium bicarbonate to aragonite? I cannot imagine how can a chemical transformation be caused by magnets. Also, why 2 magnets? How are they arranged?
 A: I found this from an article, the writer was skeptical that it truly worked.  The writer in the article says this has been a marketing scam since the 1930's.
Another common claim is that MWT causes calcium carbonate to precipitate as aragonite, a crystalline modification of CaCO3 that is slightly less stable (and more soluble) than the much more common calcite structure. Some evidence for this has been reported in the literature[⇒]. But it is not clear that the physical properties of aragonite differ all that much from those of calcite.
Permanent magnets and alternating electromagnetic fields
Most of the permanent magnet devices employ a sequence of magnets, arranged so that the water passes alternately through magnetized and non-magnetized regions. This is probably based on the experiments of Kronenberg (see below) who found that a sequence of magnets was more effective. The alternating-current devices can presumably duplicate this effect with a single coil as shown at the right. Most of these use a frequency in the 100-1000 hz region. Some excite the coil with square waves rather than with sine waves in the apparent hope that of the large number of frequency components so generated, some will be more effective than others.
A: 
How do the magnets convert calcium bicarbonate to aragonite?

They can't.

I cannot imagine how can a chemical transformation be caused by magnets. Also, why 2 magnets?

If one magnet would do it, then wouldn't two be even better? 

How are they arranged?

The magnets are arranged in such a way to separate your money from your wallet. They won't do anything to the water. 
