What is Kh/Gh?

**KaveMonster** · 09-23-2012, 01:05 AM

Hi,

I was reading about managing CO2 levels in the tank. They mentioned that the CO2 levels can be estimated by using Kh and Ph levels. So I got the API Kh/Gh kit. There are the readings from my tank and I am not able to estimate if the tank is doing ok. It has been 24 days since I had set up my 55G tank. I have lots of plants in my tank.

ph : 6.9 (using a electronic meter)
Ammonia : 0 ppm
Nitrite : 0 ppm
Nitrate : 5 ppm
Kh : 2
Gh : 6

**chocological** · 09-23-2012, 01:31 AM

Have you read the cycling stickies here?
I'd add a little bit of ammonia and test over a couple of days to see if your bio filtration is working. Other than that, looks like you can add fish :)

Just don't do what I did and add too much at once. I crashed my tank I think. :(

**KaveMonster** · 09-23-2012, 02:02 AM

Thanks... Yes I have read the them... I am just wondering about maintaining the levels. Like the CO2 thing... if it is too high (> 25 ppm of CO2) it may be toxic to the fish. I am not able to estimate it. I don't understand how the Kh/Gh/Ph thing works. There is a table out there that can estimate the CO2 (ppm) based on Kh and Ph. Some type of fish don't like to be in water with high Gh. So, I am a bit confused about this.

**kross** · 09-23-2012, 02:03 AM

Using pH and KH to estimate CO2 levels is extremely inaccurate at best. Use a drop checker, they're only about $10.

Are you injecting CO2?

**KaveMonster** · 09-23-2012, 02:17 AM

Yes. I have a diffuser and I use DIY technique with yeast to generate CO2.

**dmagerl** · 09-23-2012, 02:22 AM

Dont even think about using that chart. It is soooo wrong.

If you're not injecting CO2, dont worry about it. An empty tank (no fish) will be in equilibrium with the CO2 in the atmosphere and be about 3ppm. With fish, since they exhale CO2, the level will be a bit higher but not by much.

To answer your question, GH is a measure of metallic ions in your water such as calcium and magnesium. KH is the measure of carbonates in the water. Limestone is calcium carbonate. Water from wells that originate in a limestone aquifer will often have high GH and KH levels. Carbonates add buffering capacity to water. When adding an acid to water with high carbonates, the ph will barely budge. A tank with no KH , or no buffering capacity, will have wildly fluctuating pH.