How to test KH/GH

[Acerrato]

Hi Everyone! I purchased a liquid KH/GH test kit but have never used it before. Can you guys explain to me why we test for this and also what the readings mean? And should I do a reading out of my tap as well as a reading from the tank?

Thanks in advance!

[RogueDiscus]

Hi Amanda,
Both tests are measures of dissolved minerals in your water. General hardness (GH) measures the combined concentration of calcium, magnesium, and others like sodium and potassium in your water. The calcium and magnesium are common in well water in particular. This is what is usually being described when one's water is characterized as hard or soft. I learned the parts per million system of measurement, but the other method of degrees is also commonly used. Less than about 70 ppm GH is considered very soft. I have well water that is close to 500 ppm GH. Discus' natural Amazon environment has very soft water, however, discus in our tanks are generally very adaptable to harder water. The exception to this is when breeding. Eggs will often not hatch in GH over about 100, so breeders will use or add RO water, which has had the minerals filtered out, to lower the mineral concentration.

Kh, or carbonate hardness (Karbonate in German) measures the amount of carbonate in your water. This is often combined with the calcium as calcium carbonate. Sodium bicarbonate (baking soda) is another common carbonate source, but not usually in our water. The carbonate is the part of the chemical compound that can react with and neutralize acid in the water. The natural process of decomposing organics produces these acids, so having some carbonate is generally desirable in our tanks. Changes in the amount of acid affect the pH of the water. Discus do well in a wide range of pH values, as long as it stays stable. The carbonate then is often referred to as the buffering capacity of the water, to resist changes in the pH. In the Amazon, the water is being constantly flushed to remove decomposing matter, so the lack of carbonate is not an issue.

Since getting used to my water conditions, I have not tested for these in a long time, but it's good info to know when setting up. Hopefully someone else will fill in or correct me here, but I recall having a GH about the same as the KH means your Gh is primarily Calcium carbonate, which generally good. If the Gh is much higher compared to the Kh, then your water may have other minerals besides calcium, like sodium, in it. Sodium is usually not desirable unless being used as a treatment of some sort.

OK, too much info, and if I go on I'll probably make mistakes, so I'll stop and hopefully others will add and specifically correct any errors I may have made.

Having stable pH is desirable, so ideally your water has some Kh, preferably with an appropriate corresponding overall Gh level.

[Acerrato]

Thank you! I just tested my water and here's what I can't figure out. My pH is 6.8 (it's usually always in the 6.4-6.8 range). My GH came up as 5 but I'm having trouble determining my KH. The test says that it will turn from blue to yellow. 1st drop keeps the water kind of clear (I never see blue AT ALL)... 2nd drop turns the water clear/yellow .. 3rd drop turns the water pale yellow .. 4th drop turns the water solid yellow .. there is no color difference from drops 4-5...

I have 15, 4" Discus in my 125g - from what I've read, a GH of 5 and KH of 1-2 is not ideal for their growing - is this correct? Thank you!

Also, its important to know that I've been doing 30% water changes daily. Today I did 40%.

[RogueDiscus]

This may not be a problem at all, but it might be good to check a couple things. I looked up the API test kit instructions to refresh my memory. The drops correspond to the degree system. So that would indicate you have between 70 and 90 ppm of calcium and carbonate. If this is stable, it could be just fine. I would keep checking for a while to be sure. Being soft water that also has a low or acidic pH, I would also monitor the pH and make sure it is not dropping. I would also recommend testing your tap water for pH changes. You fill a container, check the pH, and then let it sit for 24 hrs, preferably with an air stone, and then check the pH again to see if it has change. Changes of more than about 0.2 usually means it would be good to age your water before using.

Growing fish do need some minerals, and having a GH of up to about 180 ppm, roughly 10 drops, is considered good for them. More doesn't hurt, just doesn't add.

[Acerrato]

Perfect, thanks so much! Also- I realized I posted this question in the wrong "section".. I am a newer member In the future - if that happens, is there any way for me to delete a post or at least change the category I posted under? Thank you!

[RogueDiscus]

I think your section choice was fine. It's the kind of question lots of folks might have, and tends to come up regularly. If you do ever feel the need to move or change something, you can click on the name of one of the Moderators or Administrators (see our screen names) and send us a private message.