Hey Clive
Is there any reason why it is believed that the low KH will improve CO2 absorption by the plants? And to what extent is this true?
Cheers,
Gilles
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Hey Clive
Is there any reason why it is believed that the low KH will improve CO2 absorption by the plants? And to what extent is this true?
Cheers,
Gilles
Hi Gilles,
Yes, there is a reason whose the origin is a fundamental optical illusion which is based on a very real chemical phenomenon.
The phenomenon is seen every time someone talks about the pH/KH/CO2 table.
The table appears typically as this:
The data in the table is derived from a series of equilibrium equations which begin with the basic form, something like this:
CO2 + H2O <=> H2CO3
This first equation states that when CO2 is added to water, the result is the formation of Carbonic acid (H2CO3).
Unfortunately, the fundamental flaw in reasoning occurs because everyone assumes that all the CO2 that you add immediately becomes Carbonic acid, and that as a result, in low KH water there is more CO2 because the pH is typically driven lower. These people also mistakenly assume that if you alter the KH, then that automatically means that you then also alter the CO2.
What is very much misunderstood, first of all, is that when you add CO2 to water, only a very tiny fraction of the gas enters into this equation. Depending on temperature, less than about 0.2% of the dissolved gas enters this Carbonic acid phase. This is explained more fully in the thread Stupidly used oyster shell gravel... | UK Aquatic Plant Society
Apart from all that, there is a fundamental misunderstanding of the difference between KH and Alkalinity.
So there may actually be a physiological effect on CO2 uptake performance due to Carbonate/Bicarbonate concentration levels, BUT KH test kits do not measure Carbonate/Bicarbonate content. So we really have no way of knowing. Just knowing the KH tells you nothing about how much Carbonate is in the water. Some plants may in fact respond negatively to the presence of the CO3 ion...maybe.....but the CO3 content of the water has little to no impact on the availability of dissolved CO2. This is a really important point..availability versus physiological response.
Having said that, of course, if you can see the limescale deposits caused by your tap water then that pretty much tells you that there is significant CaCO3, and water that is high in GH also typically is high in Carbonate content because, as I mentioned, the agent involved in driving the GH is usually Calcium Carbonate.
In any case, as you can see, there are many levels to this illusion. One has to do a deep dive to find the kernel of truth in order to avoid the hysteria surrounding the myths.
Cheers,
Yes, there is a reason whose the origin is a fundamental optical illusion which is based on a very real chemical phenomenon.
The phenomenon is seen every time someone talks about the pH/KH/CO2 table.
The table appears typically as this:
The data in the table is derived from a series of equilibrium equations which begin with the basic form, something like this:
CO2 + H2O <=> H2CO3
This first equation states that when CO2 is added to water, the result is the formation of Carbonic acid (H2CO3).
Unfortunately, the fundamental flaw in reasoning occurs because everyone assumes that all the CO2 that you add immediately becomes Carbonic acid, and that as a result, in low KH water there is more CO2 because the pH is typically driven lower. These people also mistakenly assume that if you alter the KH, then that automatically means that you then also alter the CO2.
What is very much misunderstood, first of all, is that when you add CO2 to water, only a very tiny fraction of the gas enters into this equation. Depending on temperature, less than about 0.2% of the dissolved gas enters this Carbonic acid phase. This is explained more fully in the thread Stupidly used oyster shell gravel... | UK Aquatic Plant Society
Apart from all that, there is a fundamental misunderstanding of the difference between KH and Alkalinity.
So there may actually be a physiological effect on CO2 uptake performance due to Carbonate/Bicarbonate concentration levels, BUT KH test kits do not measure Carbonate/Bicarbonate content. So we really have no way of knowing. Just knowing the KH tells you nothing about how much Carbonate is in the water. Some plants may in fact respond negatively to the presence of the CO3 ion...maybe.....but the CO3 content of the water has little to no impact on the availability of dissolved CO2. This is a really important point..availability versus physiological response.
Having said that, of course, if you can see the limescale deposits caused by your tap water then that pretty much tells you that there is significant CaCO3, and water that is high in GH also typically is high in Carbonate content because, as I mentioned, the agent involved in driving the GH is usually Calcium Carbonate.
In any case, as you can see, there are many levels to this illusion. One has to do a deep dive to find the kernel of truth in order to avoid the hysteria surrounding the myths.
Cheers,
Hi mate,
As I mentioned, it's really not a big problem. If you can't do the water change at a certain time, well, that's just how life goes. I really wouldn't worry about it. The most important thing is that you are changing the water. That is 1000X more important than the question of "when".
The same goes for adding the nutrients. It really doesn't matter what time of day. Obviously it does not make sense to add any nutrients just before a water change, right? Because that would just be throwing it away, but apart from that, there is no issue with what time, night or day.
Cheers,
