Yeah, the explanation in the article is completely bogus unfortunately. They have misinterpreted the chart. The confusion arises mainly because the data describes the shift in equilibrium that occurs only with the portion of CO2 that converts to Carbonic acid. But only a very small percentage of the dissolved gas actually forms carbonic acid, and this is the portion that reacts in the equilibrium equation with carbonates and bicarbonates. This explains why the dropchecker colors for example do not change very much when high carbonate content water is placed in the checker, yet the colors changes wildly if soft water is used. The carbonate/bicarbonate content acts as a buffer against the effects of the carbonic acid. This is exactly why it's no good using anything other than a known KH value distilled water in the dropchecker.
So people put high KH water in their dropchecker and add CO2. Then the dropchecker color stays blue because the carbonates absorb the carbonic acid. So, they conclude it's because CO2 is not dissolved in the water, which of course is an illusion.
KH has nothing to do with the solubility of the gas in water. Depending on temperature, only about 0.1% to 0.2% of the dissolved gas converts to Carbonic acid, so that chart you see and that explanation you're reading only applies to 0.1% to 0.2% of the CO2 in the water. The other 99.8% to 99.9% of the dissolved CO2 is unaffected by this chart.
This is so blatant. See how they cleverly weave into the fabric of their text references to their products to suck you in?
Pearl Grass prefers a little higher pH and hardness because it uses injected CO2 in the form of a bicarbonate ion (HCO3-). An addition of Brighty K, which has a pH buffering effect, is effective for preventing pH from decreasing too much.
Oh sure, just go and spend your money on our Potassium product and that will cure a problem you don't even have.
Good grief, what propaganda! Let's take a break and have a munch on a reality biscuit. Here's a tank with KH over 15 and water parameters completely opposite to what the journal tries to make you believe is optimal:
The Matrix isn't real Tom!
Cheers,