So Im wondering if acidic water naturally has more co2 for plants in it? My theory is based on this chart where lower PH seems to not need CO2 injected into the tank. Am I correct with this assumption?
The chart just tells you how much "CO2" is in the water at a given kH and pH. Nothing about how you got there. When you inject CO2, you see the pH fall. While a lot a plants thrive in low pH both with and without CO2, you can't assume that low pH water has CO2. You need to test the kH. Rainwater and RO water will have almost no kH and thus little CO2 at any pH (unless you add it). But there are many wild bodies of water that have large masses of decaying plant matter on the bottom, and I expect some have significant CO2.
I'm following what you're saying but theoretically If I have a KH of 3 and a PH of 6.8 in my tank then according to the chart I have some good CO2 levels in it regardless of me ever hooking a CO2 tank up to it? The main thing to watch for is the KH/PH relationship? If you were lucky enough to have a great KH/PH relationship going on you wouldn't need to add CO2 to the water with a tank? Thanks for your insight.
A good question I have is regarding GH. I understand the relationship of KH to PH but don't really understand where GH plays it's part. Let's use my example from above. If I have a PH of 6.8 and a KH of 3 then I'm looking pretty good in CO2 ppm's. Now, in my KH, GH test kit why don't I just chuck the GH test solution in the trash? I understand it tests general hardness but if it's really the KH we're concerned with then how concerned should I really be about the GH side of it. I know GH and KH are supposed to be the same in most circumstances but mine is not. My KH is low and my GH much higher. My KH is about 3 and my GH is around 6. Does this matter? How does this affect my plants and can I in a sense not worry about the GH as long as my KH is in range? Thanks again for your time and experienced help.
gH is the positive ions, the Mg+2, the Ca+2. The kH is the negative ions, CO3-2 + 1/2 HCO3-.
If you just dissolve CaCO3 in the water, kH and gH will be about the same. But if you inject CO2, the gH won't change.
Now you've about reached the limit of my knowledge. You don't have to have CO2 to have a thriving planted tank. I understand that what mattes is the balance. The nitrate, "carbon", ferts, and light must be matched with what your plants need. If there is more of one thing, it will feed something else, like algae, because the plants can't grow faster without all of the things they need in proportion.