05-03-2011, 12:06 PM
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This is very involved. And altering GH or KH may not be necessary. First thing, is what the hardness in your source water (I assume tap water) is. You can find this out from your water supply people, many have websites but if not they can tell you. Ask for GH and KH [I'll explain these in a moment]. If they have a website and you can't figure it out, give me the link and I'll take a look. No point in wasting money on expensive hardness test kits if you only use them once; as I say, we normally work within what we have coming out of the tap, and there are ways to alter this if necessary.
GH is general hardness, basically referring to the mineral salt content of the water. In this context, "salt" refers to mineral substances other than our common table-type salt. Calcium and magnesium salts are the most prevalent minerals for hardness, but many others are involved too. The source of the water determines what mineral salts are present, as water picks up minerals from the rock over which it flows. GH does affect fish, as much as pH, sometimes even more, so it is important to know the GH of your tap water. In an aquarium, GH will not change unless you specifically force it by some means. Will leave that for now.
KH is carbonate hardness; spelled with a "K" because carbon is karbon in German and that's where the science came from. This is the measurement of carbonates and bicarbonates in the water. It is connected to GH, and a high GH usually carries a high KH, but not always. The chemistry is for me complicated, but as long as we understand the principle we are OK. The KH has absolutely no impact on fish. But it is important as a buffer of pH.
GH, KH and pH are inter-connected. The harder the water, usually the more carbonates/bicarbonates. And the higher these are, the more they "buffer" pH by preventing it from altering. This is why chemical pH adjusters frequently fail, or worse cause fluctuating pH levels too quickly. The natural KH buffering capability in the water will resit (prevent) permanent shifts in pH, until such time as the buffering is exhausted, and then the pH can crash badly.
Natural processes in nature and in the aquarium cause the pH to shift diurnally every 24 hours. This is not harmful to fish, it is natural. But we don't want it shifting too much, that can be dangerous.
To return to my opening comments, the GH and KH of your tap water must be known before we can consider what, if any, adjustment may be needed. All fish have preferences for GH and pH, but many are somewhat adaptable within a general range. Some are very specific, such as livebearers and rift lake cichlids requiring harder water and a correspondingly higher pH. We can discuss this more when we know where we stand.