[Rex Grigg]

The crushed coral would have no effect on the pH/KH/CO2 relationship.

Do you you have driftwood in the tank? Peat? What kind of substrate?

Are you sure about your test kit readings?

The simple fact is if you are not injecting CO2 you don't have more than about 3 ppm.

Also if you have crushed coral in the water then your pH and KH should be higher than that.

 

[Rex Grigg]

Excel is NOT CO2. So it doesn't show up as CO2.

Driftwood can and does leach chemicals into the water column that lower the pH.

What are your source water parameters?

 

[Rex Grigg]

Oh... the light bulb comes on!

Baking soda will raise KH but also raises pH.

TANSTAAFL = There Ain't No Such Thing As A Free Lunch.

The pH of your source water will vary a bit as it doesn't have a lot of buffer. Try doubling the sample size on your KH test kit (10 ml of water instead of 5). That will make each drop equal 0.5° of KH.


KH is going up from the crushed coral and the pH is going down from the driftwood.

 

[Rex Grigg]

All driftwood is going to leach something into the water. It's just the way it works. You can boil it but that probably won't fix the problem.

 

[Rex Grigg]

Pretty much.

The whole CO2/KH/pH chart is based on the assumption that the only buffers in the water are bicarbonate based and the only thing lowering the pH is the CO2.