10-23-2010, 01:24 PM
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I do not believe the goldfish will have problems with your water, compared to some tropicals; and after 8 years I suspect any issues would have occurred by now.
As for the Tetra kit, I am not familiar with it. GH and KH are two different things, though related; and pH is also related to these.
The KH has no effect directly on fish at all. KH is the amount of carbonate hardness in the water, and the more there is the more it "buffers" the pH, preventing it from dropping (acidifying) as it would otherwise tend to do due to the biological processes. So a high KH means your pH is going to remain stable. This is important for two reasons, first the pH will not fluctuate (and fish prefer pH stability), second you would find it difficult to lower the pH if you wanted to as for soft water tropical fish. I wouldn't worry about goldfish if it is stable.
The GH is the general hardness, a measure primarily of the amount of calcium and magnesium in the water. This does affect fish, internally, if they are soft water fish being kept in hard water for instance, or in reverse if they are hard water fish being kept in very soft water. Again I would not fuss over your goldfish if it is relatively stable.
I won't go into more detail as I don't think you have cause to be attempting to change the hardness/pH.