However, whether the CO2 gas is dissolved or not may not matter at all, all that matters is that enough CO2 gets to the plants.
If you add say 3 bubbles per second in a a tank with a KH of 10 and another with a KH 1, you still add exactly the same amounts of CO2 gas, pH is not even considered here, go directly to CO2.
A ph/Kh combo of 6.0 and 1 = 30ppm
A pH/KH combo 7.0 and 10 = 30ppm
It takes the same amount of CO2 gas to get 30ppm from ambient conditions, yes, the CO2 can have differing solubility at different KH's, however, this is not going to make any real practical differences to plants or the CO2 system.
It does make some differences in natural systems where CO2 is not enriched like we do it often in CO2 planted tanks, subtle changes can make differences there, but not in our aquariums.
This is where practical applied knowledge and consideration comes into play versus trying to compare things to natural systems and relationships. While true is some regard, it has virtually no effect near as I can tell using a a wide range of KH's and CO2 meters over the years. I've had less than 1 Kh to upwards of 12 degrees for several years at a time, a few plants are weak at higher KH's, but it had nothing to do with CO2.
Temperature decrease also increases the ability for water to hold more dissolved gas(all, not just CO2) as well.
Higher you go, the more steam and boiling water vapor you get.
I think this is a big issue for folks that tend to use RO water/and keep Discus, they tend to use higher temps, then have large fish, all issues when it comes not only to CO2, but O2 as well.
To increase O2, often they increase the wet/dry filters, add more surface turn over, but this has nothing to do with KH does it?
Nope, not one bit.
I know much more about saltwater systems and CO2 unfortunately, but the balance of these carbonate species (which ultimately affects the solubility of carbon dioxide), is dependent on factors such as pH. In seawater this is regulated by the charge balance of a number of positive (e.g. Na+, K+, Mg2+, Ca2+) and negative (e.g. CO32- itself, Cl-, SO42-, Br-) ions. Normally, the balance of these species leaves a net positive charge. With respect to the carbonate system, this excess positive charge shifts the balance of carbonate species towards negative ions to compensate. The result of which is a
reduced concentration of the free carbon dioxide and carbonic acid species, which in turn leads to an oceanic uptake of carbon dioxide from the atmosphere to restore balance. Thus, the greater the
positive charge imbalance, the greater the solubility of carbon dioxide. In carbonate chemistry terms, this imbalance is referred to as alkalinity.
So harder water will have higher solubility of CO2.
CO2 dissolved in the ocean immediately reacts with water to form carbonic acid. Most of the carbonic acid gives up a
proton (H+)…dissociates…to form bicarbonate. Some of the bicarbonate dissociates to form carbonate. Thus harder water holds more or put another way, CO2 is more soluble in harder water.
As far as use of CO2 required for a tank, this is
another area.
Refer to Fick's 1st law of diffusion.
This is really the biggest issue for us, not so much the KH, that's more for certain species of plants and fish.
Diffusion is the biggest issue and the ability for the CO2 to get to the plants is the primary driver here.
More current = more off gassing, however it also means less boundary layers and better CO2 delivery/mixing and harder for many species fo algae to attach, less detritus on leaves providing fuel for algae and other periphyton growth.
More current also means more stable O2 levels and often higher levels.
So this is a trade off, one long ignored and neglected at the expense of the fish and plants.
We can add a tad more CO2 and get the benefits of more stable O2, better CO2 delivery, better mixing and less algae/dirt in our tanks.
This seems to be a good trade off to me.
If you can, a lower KH is nicer for more plant species, most every hard water plant can do very well in soft CO2 enriched aquariums(I've not found one to date that cannot do well). But low KH is not going to save folks from algae or CO2 woes.
Just keep that in mind there.
CO2 and alkalinity are the two least understood topics in this hobby.
Even back in the mid 1990's folks where telling others to watch how they measure CO2 and the KH issues:
http://www.thekrib.com/Plants/CO2/hardn ... frank.html
Read bottom of the page. I had pretty high PO4's in my tap back then and ignored the pH/KH and went with fish and plant responses for 30ppm(later determined using RO reconstituted).
Hope this helps, likely confuses, but the bottom line is worry more about the Fick's 1st law than solubility.
As far as fish and perhaps a few plant species, focus on lower KH's 3-5 seem okay for most so called low KH plants.
Folks that claim super low pHs and low KH's in the 5.5-6.0 ranges or KH's at 1 or so are required for any plant full of beans. Look for advice elsewhere.
Regards,
Tom Barr
guess not!!
