Gh Lower Than Kh

I have been using nt labs test kits for some time but I am confused by results I have recently got .According to the kits instructions the gh test measures total hardness which includes the alkaline hardness (kh) so it should not be possible to have a GH that is lower than the KH. I have four aquariums and all now show a GH that is 1-2 units below the KH. Is this possible or do I have a faulty kit?. I have been using these kits for a few years but until now my GH has usually been 1 degree above the KH. My tap water is very soft and I Add quite a lot of KH up to get the pH stable and at the right values for the fish. I do not add anything to raise the GH. Is it normal for a GH test to include the KH?. Is there any need to increase GH or is it only the KH that is important. Any ideas please.

 

You can have whatever values for each - they are not bound by one another.

gH = combination of Ca+ and Mg+
kH = CO3-

ex: 100% RO water. Boost kH using KHCO3 (no calcium or magnesium) to 3 degrees.
Now, gH boost to 2 degrees using CaSO4 and MgSO4 (no CO3- preset).

This water now has a kH higher than gH.

 

You can have whatever values for each - they are not bound by one another.

This I agree with.

gH = combination of Ca+ and Mg+
kH = CO3-

This isn't quite correct. KH = carbonates and bicarbonates (CO3 and HCO3)

When GH and KH are similar, it is usually because calcium and magnesium are the main sources of carbonates and bicarbonates. However, other things can contribute to KH that won't be reflected in GH. Some examples would be pottassium carbonate and sodium bicarbonate. If either of these (but not limited to these) are present, the KH can be higher than GH. Other sources of carbonates and bicarbonates can also do this.

ex: 100% RO water. Boost kH using KHCO3 (no calcium or magnesium) to 3 degrees.
Now, gH boost to 2 degrees using CaSO4 and MgSO4 (no CO3- preset).

This too would be true though, because as you state...no carbonate or bicarbonate present.

 

This isn't quite correct. KH = carbonates and bicarbonates (CO3 and HCO3)

Whoops, yes you are right... long day.... I should have said carbonates / bicarbonates instead of CO3- my bad.

 

Thank you for clearing that up. Is there any real advantage in increasing GH for fish that seem happy with the level it's at ( around 3 to 4 )

 

Thank you for clearing that up. Is there any real advantage in increasing GH for fish that seem happy with the level it's at ( around 3 to 4 )

If you have soft water fish, a GH of 3 or 4 may be all they need. I wouldn't recommend trying to breed guppies or other live bearers in soft water, nor would I recommend keeping African cichlids in that water, but many other fish species would do well. Discus, cardinal tetras and many other tetras for example as well. It is easiest to keep the fish that are suited for our water so that we don't have to monkey with parameters, and many aquarium fish species do well in a wide variety of water parameters, which helps make it less necessary.

Whoops, yes you are right... long day.... I should have said carbonates / bicarbonates instead of CO3- my bad.

I don't often go into ways to boost GH and not KH, so I very much enjoyed that addition in your post. I also very much liked the fact that you are aware that GH and KH are independant from each other, which many people don't get, due to the fact they are use to calcium and magnesium making up both hardness levels.

 

I don't often go into ways to boost GH and not KH, so I very much enjoyed that addition in your post. I also very much liked the fact that you are aware that GH and KH are independant from each other, which many people don't get, due to the fact they are use to calcium and magnesium making up both hardness levels.

I use KHCO3 to boost my water to ~ 1 degree of kH and then a combo of CaSO4 and MgSO4 to yield 30ppm Ca and 10ppm Mg (6-8 degrees of gH). Mostly in it for the plants, fish don't seem to mind the soft water either.

 

One of my tanks

If you have soft water fish, a GH of 3 or 4 may be all they need. I wouldn't recommend trying to breed guppies or other live bearers in soft water, nor would I recommend keeping African cichlids in that water, but many other fish species would do well. Discus, cardinal tetras and many other tetras for example as well. It is easiest to keep the fish that are suited for our water so that we don't have to monkey with parameters, and many aquarium fish species do well in a wide variety of water parameters, which helps make it less necessary.

Thank you. I am breeding guppies in one of my tanks. So far I have had quite a few fry some of which are now about 6 weeks old and seem ok. Do you think I should make the water in this tank harder?. If so what would you recommend using to do this

 

When I was breeding guppies I used something very similar to this.

 

I bump up my hardness and pH with wonder shells and baking soda ..

 

One of my tanks

Thank you. I am breeding guppies in one of my tanks. So far I have had quite a few fry some of which are now about 6 weeks old and seem ok. Do you think I should make the water in this tank harder?. If so what would you recommend using to do this

I wouldn't automatically try to fix anything that seems to be working for someone. But I would say that careful observation might suggest something needs to change if something isn't working, and having some idea of what to try changing can alleviate a lot of stress. So for now, I'd say observe. If you notice problems or unsatisfactory results such as infertility, miscarriages, sickly fish, deformaties, shortened lifespan or fish that just don't seem to be as hardy as they should be, then something needs to change. So, lots to look out for, for sure, but many breeders keep challenging the "norms" in order to make fish that can tolerate those wider parameters that I mentioned earlier, so I hesitate to jump on a "must do" mentality bandwagon, because I know that there isn't always just only one way to do anything.

 

Thank you everyone for the advice. I will just observe for now but I now know what to do if problems occur.