# [Wet Thumb Forum]-GH and KH



## aquabillpers (Apr 13, 2006)

I've keeping aquatic plants and fish for a number of years, with generally some success except for a few disasters. However, as one gets older he learns that some things that were "true" years ago are no longer so.

For example, take GH and KH. I always though that the amount of dissolved carbonates (GH) was what influenced the growth of plants and the keeping of some fish like discus and the breeding of more. The main role of KH was to prevent rapid changes in PH. It had little direct effect on plants and fish.

Lately I've been seeing posts that contradict this. So my questions are:

What is the effect of high and low GH on plants and fish?

what is the effect of high and low KH on plants and fish.

Thanks.

Bill


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## Roger Miller (Jun 19, 2004)

In the aquarium hobby we probably over emphasize the importance of GH and KH. Partly that is because GH and KH are easily measured, while other factors that may be more important (stress from over crowding, for instance) are difficult to measure.



> Originally posted by Billpers:
> What is the effect of high and low GH on plants and fish?


First, GH is not the amount of dissolved carbonate. It is the concentration of calcium and magnesium, expressed as the equivalent amount of calcium carbonate. Carbonates may or may not be present in the water.

For plants, calcium and magnesium are both essential nutrients. Their concentrations do not have to be high in order to satisfy plant demands, but being high doesn't seem to have an effect on plants. It *is* important that calcium and magnesium are balanced. If the magnesium concentration is too high compared to the concentration of calcium then it may block plant uptake of calcium.

I'm not sure about fish. My understanding is that most "soft water" fish -- discus in particular -- can be healthy and breed over a considerable range of GH. I've also heard that there may be some effect with calcium and/or magnesium on sensitive membranes, but as far as my knowledge goes that is simply rumor. It seems like if the membrane effect were important then it would not be possible for the fish to be healthy or breed successfully in hard water.



> what is the effect of high and low KH on plants and fish.


For plants in nature bicarbonate is an important source of carbon. Plants don't use it as long as CO2 is available and probably don't use it unless specific environmental triggers are present. They also don't seem to use it unless the light is very bright. What's more, when they do use it, the pH gets very high. All in all, direct use of KH by plants is probably not very important in aquariums and is usually discouraged when it happens.

Aside from that the primary role of KH is just to buffer the pH. I don't know what other direct effect it my have on plants or animals.

There is also a salinity effect if GH and/or KH is extremely high. Normally, this means water that is more saline than any tap water. Also, if salinity is a problem then sodium, chloride and sulfate are more likely problems than are GH or KH. When the salinity is too high fresh water fish and plants have trouble maintaining the correct balance of fluids and minerals in their bodies. Fish and plants adapted to salt water have the same effect in reverse if the salinity is too low.

To some extent plants and animals can adapt to a wide range in salinity, but the variation needs to be gradual.

Roger Miller


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## TWood (Dec 9, 2004)

Hey Roger,

I got my water report and it says:

Calcium: 83 mg/L
Magnesium: 50 mg/L
Sodium: 21 mg/L
Total Hardness as CaCO3: 410 mg/L
Chloride: 19 mg/L
Sulfate 132 mg/L
Dil. Conduct (umhos/cm): 942
Tot. Alk. s CaCO3: 302
Bicarbonate: 368
Dissolved solids: 510 mg/L

That's a 1.7:1 Ca:Mg ratio. Not good?

Is that sodium level a concern?

Any of the other parameters particularly wonky?

Thanks,

TW


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## aquabillpers (Apr 13, 2006)

Roger,

Thank you very much for your reply. As always it was informative.

My planted aquaria are "natural" tanks and usually soil based. As such, the KH is more important than it might be to those who supply carbon by injected CO2 and reduce the PH in the process.

I believe that the amount of dissolved CO2 in an aquarium drops substantially as the PH rises, approaching zero as the PH rises above 8.5. Is this correct? In my tanks I try to keep the PH reasonable by controlling the KH, keeping it at 2 or 3 degrees.



> . . . For plants in nature bicarbonate is an important source of carbon. Plants don't use it as long as CO2 is available and probably don't use it unless specific environmental triggers are present.


Do all plants respond this way? I've read that vals in particular "eat" KH, and I've observed KH dropping in tanks that had rapidly growing val populations. My impression was that most plants didn't do that.

So, if I may summarize what I understand from this:

1. Under certain circumstances, some plants will consume KH if there is not enough CO2 available. Except for that, the only effect of KH is to control the changes in PH.

2. GH is the main source of certain minerals for plants and might effect the health and breeding of a very few fish. To most domestic fish it is not too important.

Thanks again.

Bill


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## Roger Miller (Jun 19, 2004)

> I believe that the amount of dissolved CO2 in an aquarium drops substantially as the PH rises, approaching zero as the PH rises above 8.5. Is this correct?


All else being equal, yes.



> Do all plants respond this way? I've read that vals in particular "eat" KH, and I've observed KH dropping in tanks that had rapidly growing val populations. My impression was that most plants didn't do that.


I doubt that all plants respond that way. Not even all plants we keep in aquariums respond that way. I do suspect that most of the plants that are adapted to prolonger submersion will use bicarbonate under some conditions. Many of the plants that we grow in aquariums aren't all that well adapted to prolonger submersion.

It's a detail, but the vals themselves don't "eat" the KH. The information I've seen indicates that plants -- and vals in particular -- use one or two different mechanisms to extract CO2 from bicarbonate, like this:

2HCO3- -> CO2 + H2O + CO3--

The use the CO2 that is produced. The amount alkalinity due to carbonate (CO3--) on the right side of the formula is equal to the alkalinity due to two bicarbonates (HCO3-) on the left side of the formula, so there is not change in alkalinity.

What happens, though is that the carbonate reacts with calcium in the water, forming calcium carbonate "marl." The marl precipitates -- sometimes directly on the plant leaves -- and removes the carbonate from solution.

The KH drops because of the precipitation of calcium carbonate, which is not a direct effect from the plant. If the water is very soft then the marl won't form. The KH won't drop, but the pH will skyrocket because of the carbonate in the water.



> So, if I may summarize what I understand from this:
> 
> 1. Under certain circumstances, some plants will consume KH if there is not enough CO2 available. Except for that, the only effect of KH is to control the changes in PH.
> 
> 2. GH is the main source of certain minerals for plants and might effect the health and breeding of a very few fish. To most domestic fish it is not too important.


That is as I understand it. Please keep in mind though, that I know less about fish then a lot of other people.

Roger Miller


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## aquabillpers (Apr 13, 2006)

Thank you!


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## kam (Nov 23, 2005)

> Originally posted by Roger Miller:
> 
> 
> > I believe that the amount of dissolved CO2 in an aquarium drops substantially as the PH rises, approaching zero as the PH rises above 8.5. Is this correct?
> ...


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## Roger Miller (Jun 19, 2004)

> Originally posted by Kam Wong:
> Can you tell me more about the marl? as I have had my pH increase rapidly over time and the GH has also skyrocketed, thus melting of Tonia sp.'s.


Kam,

Marl formation removes calcium and carbonate from the water. When marl forms the GH and KH both drop. The pH goes very high; values over 9 are normal.

If your GH and KH are increasing then the most likely source is in rocks, substrate material or decorations in your aquarium. Before you go to any length to remove the GH and KH you first need to identify and remove the source.

Roger Miller


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## kam (Nov 23, 2005)

Roger,

Thanks for the suggestions, but my tank does not contain any rocks or decorations. Substrate is Elos with JBL bottom fertilizer. So far my other tanks have not had this problem with the same substrate. 
Could if be affected by TMG, Kent Micro & K that I am dosing.

Kam


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## Roger Miller (Jun 19, 2004)

> Could if be affected by TMG, Kent Micro & K that I am dosing.


Probably not. You can check the ingredients, but I don't think those products contain significant amounts of calcium, magnesium or bicarbonate.

Snail shells when they dissolve will increase KH and GH, as will other types of shell.

Not all lots of substrate products always have the same characteristics. See recent discussion on Eco-Complete. It is possible for the same product to produce different effects in different aquariums.

Over a long period of time evaporation of water and replacement with tap water can result in increase GH and KH, but that is rarely a problem.

Roger Miller


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## kam (Nov 23, 2005)

thanks Roger,

I'll have to monitor the situation and hope to stop the increase in GH before all my Eriocolons and Tonias melt away.


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