Brita type filter, hardness and alkalinity

I have one of these jug-type filters to filter drinking water. The
water that comes out has much less alkalinity and a lower pH. Is it a
good or bad idea to filter water through this for my tanks? (My tap
water is very hard and has high alkalinity siro 450ppm hardness 300ppm
alkalinity). I also boil some of the water for my changes, but the
kettle is pretty furred up and when inverted over the bucket flakes of
limescale get in. Are these harmful?
Local hardware shops sell things to prevent this scaling in the
kettle, they are tangles of a shiny metal, looking like swarf or a
coarse wired brillo pad. Does anyone know what they are made of, how
they work ie by puuting something into the water to soften or taking
something out. Again does anyone have any thoughts about ramifications
in the aquarium?
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