I use a hammer and chisel
Honestly though, as far as I know, RO/DI units are the only things that can be effective against the hardness of our water... everything else just doesn't work or carry their weight in cost.
Water softeners won't do squat, all they do is replace one mineral with another to prevent calcium buildup on our water outputs. Most other methods are generally reserved for FW tanks (ie. use of tannins via peat filtration, driftwood, etc.). Chemicals are out of the question for nearly all experienced aquarists for a good reason.
I use RO water for my reef and straight out of the tap water (treated with prime) for my FW tanks.
-Richer