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Hello!
I really want to know how I can reduce the GH ( General Hardness ) from my Corydoras tank. I am using RO Machine, but it still can not help me to reduce GH. My RO machine reduce lots of KH ( Carbonate Hardness ) from 20 to 6. That is prefect for me, but GH ( General Hardness ) it won't change. Can anyone tell me what I have to do for this case, or my RO machine is not good enough. I really want to change GH for my tank. My city water is so so alkaline GH and KH are over than 20, so I am trying to reduce them as possible as I can. Please! help. Thank you very much.

Bunthid or Max

1) Ignore GH. It's a measure of how much ions with 2+ charge there is in the water. It's originally intended to allow calculation of how much limestone scale will form in steam engines, and is not an interesting or useful measure for aquaristics.

2) Your RO does reduce GH. If your test kit says it doesn't, there is something wrong with your test kit.

In short: Don't worry, be happy - and throw away that GH test.

Mike_Noren wrote:1) Ignore GH. It's a measure of how much ions with 2+ charge there is in the water. It's originally intended to allow calculation of how much limestone scale will form in steam engines, and is not an interesting or useful measure for aquaristics.

2) Your RO does reduce GH. If your test kit says it doesn't, there is something wrong with your test kit.

In short: Don't worry, be happy - and throw away that GH test.

Mike,

I have to be "devils advocate" here.

I do agree that a correctly working RO unit should remove GH (as well as KH, and as the latter is happening, I do agree that the GH test is not working right).

In one way I also agree that GH is not a particularly useful thing to measure - but not because 2+ ions are meaningless in aquariums. What I do agree is that measuring only 2+ ions is pretty pointless, as 1+ or 3+ ions should also be considered. The better thing to measure is the conductivity of the water, which is a measure of all the IONS in the water.

We can of course debate whether conductivity (or any other way to measure ions in the water) is important or not for the fishes. I think that conductivity is an important factor for the wellbeing of and ability to breed their fish. However, many fish will happily live way outside their "normal" range when it comes to water conductivity.

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Mats

It has been suggested to me that one should use a water softener and then run the softened water through the R/O unit.

Jackster wrote:It has been suggested to me that one should use a water softener and then run the softened water through the R/O unit.

That will prolong the lifetime of the RO membrane, because the sodium chloride is "easier to flush out" than some of the other salts that you may have in the water. But the RO membrane will stop all salts from passing through it equally, so it's just a bit of saving on the life of the RO membrane that is the difference.

Btw, a water softener will also remove KH, as it's not particularly fuzzy about what it removes. It's working on an ion-exchange principle, where sodium and chloride is replacing other cation and anion compounds.

--
Mats

MatsP wrote:

Mike_Noren wrote:In one way I also agree that GH is not a particularly useful thing to measure - but not because 2+ ions are meaningless in aquariums. What I do agree is that measuring only 2+ ions is pretty pointless, as 1+ or 3+ ions should also be considered.

Yes. The total amount of ions is an interesting measure; the amount of +2 ions on its own is not.
GH, unfortunately, is a measure of the amount of +2 ions. Sodium ions, for instance, do not affect GH (although chloride may poison the reaction chemicals).

The better thing to measure is the conductivity of the water, which is a measure of all the IONS in the water.

Absolutely. Conductivity is in my opinion THE most important measure for aquaria, more so than even pH and KH.

We can of course debate whether conductivity (or any other way to measure ions in the water) is important or not for the fishes. I think that conductivity is an important factor for the wellbeing of and ability to breed their fish. However, many fish will happily live way outside their "normal" range when it comes to water conductivity.

That is true for all water parameters; the reason I consider conductivity the most important parameter is because while it is impossible to kill a fish by pH shock or by keeping it at the wrong pH (at least as long as you're in the 6.5 - 9.5 interval), it is easy to kill a fish with conductivity shock.