04-06-2010, 05:20 AM
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Well, pretty much a high pH goes hand-in-hand with hard water. If you've got soft, acidic water and you want harder, alkaline water, you can add do stuff like used crushed coral or aragonite sand as your substrate, use limestone rocks as decor, use dolomite or crushed coral as filter media, etc. If you're trying to go the other way around, using peat in your filter can lower the pH and hardness a little bit but won't make much of a difference if your water is very hard. You can also buy an RO (reverse osmosis) machine which removes the ions that make your water hard and in the process moves the pH to neutral to slightly acidic. From there, natural processes in your tank, possibly with the addition of peat, can lower pH more effectively. RO machines are expensive and kind of a pain, so in general I'd say it's much easier to make soft water hard than the other way around.
Though these methods do exist, they are a lot more work and can be rough on your fish, especially if water changes introduce water that's noticeably different from what's in the tank. I definitely think you're better off stocking your tank around your tap water parameters than resorting to the above methods.