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Old 03-18-2010, 10:37 PM   #3 (permalink)
Diana K
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Default Re: Understanding GH & TDS & Hardness

It is not so simple as just adding things up. The GH test for example compares the things it is testing to calcium carbonate.
Similarly the Ca and Mg tests may not report Ca and Mg, but some other equivilant. (Sorry for being so vague, it has been a while since I have looked into these details)

My tap water is just under 300 ppm per my TDS meter, and my soft water fish that were hatchery raised are OK, including Discus, but I need RO for German Blue Rams.
GH and KH are around 4-5 German degrees of hardness, and these do not add up to 300 ppm, either, but under 200 ppm, even on a day when both are reading 5 degrees.
My hard water tanks (Lake Tanganyika) has a TDS closer to 800 ppm. My Brackish water tank (SG 1.004) has a TDS of about 2000 ppm.

I would call your water fairly soft, fine for hatchery raised soft water fish, but look into RO for the most delicate fish, and for breeding soft water species.

Last edited by Diana K; 03-18-2010 at 10:52 PM..
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