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Re: Nitrates (actually, KH/pH/CO2)

Ok, this is TOTALLy non-scientific, but here's how I think of the relationship between KH, pH, and CO2.

First, imagine a seesaw - you know, that thing you rode on as a kid in the park, and when she was feeling mean, your friend jumped off when you were at the top and you thumped down on the ground really hard...got it?

OK, well I think of KH as a box on the right side of the seesaw (some people call them teeter-totters). And I imagine there's a stick on the left side, which is marked off in pH increments (are you seeing this?). When the left end of the seesaw is on the ground, it's pointing at pH 6 on the stick, and when it's at the top, it's pointing to pH 8. There's also a container on the left side for adding CO2 - we'll call it the CO2 side. It helps to imagine that CO2 has weight.

Ok, here we go. When you add CO2 to the CO2 side, it will make that side go down, lowering the pH. But if there's alot of KH is in the KH box (say, KH=8), that makes it harder for the CO2 side to go down - imagine a small child on the KH side of the seesaw vs. an adult. You need alot more pressure on the CO2 side to move the seesaw if there's an adult over there! The greater the KH, the more CO2 you need to add to change the pH. That's why people recommend a KH of 3 or over when adding CO2 - less than that, and the seesaw can swing really fast, and your tank thumps down really hard to a very low pH.

So you can see that as KH gets larger, it takes more CO2 to cause a pH change. This is seen at http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html, especially by looking at the 3rd figure. And you can also visualize how adding more baking soda, which puts more weight on the KH side, does nothing to change how much CO2 is in the imaginary box (that is, available to your plants) - it only makes the pH side of the seesaw go up.

I hope this helps & didn't just confuse you!


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