I would get the new Maxtra cartridges. The claim is they filter more calcium. Also, see this, as the instructions have changed for these new Maxtras.
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| Maxtra cartridges require no pre-soaking and there is no need anymore to keep the cartridge immersed in water. | |
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http://www.brita.net/maxtra/handling.html?L=0 and watch the video; they say you need to use cold water.