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Old 06-26-2010, 03:33 PM   #1
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KH and GH question, different specs in different reference locations?

Hey guys. Recently I've been researching what my fish like to live in water hardness wise. Here's what I've found..

First number is dGH from Baensch Aquarium Atlas Volume 1, second is GH/KH from the API GH/KH test kit, and third is a KH suggestion from live aquaria.
  • Guppies: 10-30, 4-8, 10-30(KH)
  • Zebra Danios: <30, 4-8, 8-12(KH)
  • Bloodfins: <30, 4-8, ?
  • Betta: <25, 4-8, 0-25(KH)

First off, dGH is just degrees GH aka degrees of hardness? It's just weird cause it says 10-30į dGH. So that'd read 10-30 degrees of degrees general hardness? A bit confusing. (Ok wikipedia confirms it's degrees of general hardness, bit of a repeated unit there.)

Ok, so which number should I go by? Also, if you know my tank at all, I have plants, and they don't like really hard water. According to The Atlas, my plants, on average, like a KH of around 10. (Anywhere from 6 to 15).

I know that GH and KH are different. GH (General Hardness) measures Ca2+ and Mg2+ and stuff like that. KH (carbonate hardness) measures CO32- and it's conjugate, so they are, in fact, two different measurements. Why does live aquaria only give KH? I've read that when you only get one measurement you should just match the other one to it as well. But in my case that doesn't work, cause my plants don't like really high KH. Generally, when I read about plants I get KH and when I read about fish I get GH. (Of course carbonate decomposes into CO2 eventually, so I can see that point). I'm just a bit confused that's all. I mean I have the ability to make my GH 15 and my KH 10, as those are the average from the Atlas with my fish (GH) and plants (KH).

I was just worried cause in the directions in the API kit, it says 11-20 (GH or KH) is for marine fish and inverts. Freshwater fish are from 4-8 and plants are like 2-6 or something like that.

Can somebody set me straight?

And yes, I know, constant water parameters are much better than fluctuating ones. Please, that's not the discussion here.

EDIT: Just found out I don't have a choice regarding adjusting these values. The GH out of my tap is 1 (water softener doin it's job) and the KH is 5. So even if I did just add some tap water, it wouldn't nearly bring my GH to any value that anything (fish or otherwise) would like.

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Old 06-28-2010, 07:36 PM   #2
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It has been my experience that unless the water is acid or base enough to melt them, most fish will do just fine with a given set of parameters as long as they are consistent. Having done planted tanks myself...I would say do what you need to do to make the plants the most happy and they will in turn make your fish happy
Hope that helps....by the way...I had water that was high in GH and KH and my plants loved it...so it's really a trial and error type of experience for your individual situation. For example I had a large planted tank in hard water with discus and angelfish...the books say keep them in pH of 6.0 and low GH and KH...all of them grew quickly and thrived. So I don't really believe there are any hard and fast rules...breeding may work a bit differently but if you are mainly looking for display purposes I think you will be fine with the parameters you have.
I think most fish and plants prefer to take in the nutrients and dissolved minerals in water that is higher in GH and KH, that has been my experience.
You might look into specific dry fertilizers to give your plants what they need in terms of minerals.
Have you checked into the EI (Estimative Index) Method of fertilizing?
I think the main thing you have to worry about with a GH of 1 and KH of 5 is a pH swing or crash...if there is not enough mineral in your water to provide that buffer you may need to add some.
I would post this on the planted tank sub-forum and you will probably get more information relative to hardness.
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Old 06-28-2010, 07:55 PM   #3
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Any recommendations in an atlas type text are obsolete for captively raised fish and all of the listed species are predominantly farmed.

You probably don't want to be using "softened" water in your tanks. I suspect your readings are a bit out of whack because of it. I really hope one of the chem geniuses are around....
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