I was waiting for this question long time a go.
There is a wrong belief that changes of temperature have
significant effect to the CO2 levels in aquariums. Reality is: There is some effect, yes, as solubility of gases in water is a function of temperature: the higher the temperature, the lower the oslubility. But, one thing is this, and another that a change of 5 to 10 degrees has a significant effect.
To be more precises, CO2 solubility as a function of temperature follows this behavior:
The scale is a bit tricky, but not match. It is related to solubility in % (gr every 100 gr) but we can translate this to ppm by multiplying by 1000 (to pass from gr to mg) and by 10 (to pass from 100gr to 100 gr). Doing so, you notice that, a normal temperature of an aquarium (25 degrees). solubility is about
1450 ppm.
Now, if we increase temperature in 5 degrees, up to 30, solubility goes up to 1250 ppm. Or we are going go go crazy and say tempeture water reaches 40 degrees. Solubility becomes into about 1000 ppm.
Now, CO2 diffusion process is linked to the relative concentration of CO2 in water respect to the saturation point. Levels above are those in which no more CO2 will dissolve in water, what would drive formation of CO2 bubbles in water.
But considering the three values of solubility, and asusming that we have the 30 ppm in water, the percentages of saturation are:
25 degrees => 100 * 30 / 1450 = 2.07%
30 degrees => 100 * 30 / 1250 = 2.40%
40 degrees => 100 * 30 / 1000 = 3%
So, even increasing temperature up to 40 degrees, we are not reaching anymore than a 3% of the maximum limit. This will have not significant impact in CO2 levels in the tank.
However, there is a reason why temperature can be an issue, and it is related to the enzymatic behavior of the photosynthesis. Enzymes are catalysts of chemical reactions and as such, their activity increases with temperature. This means that more CO2 can be uptaken by plants at higher temperatures. Some studies have proven that the maximum rate of photosynthesis, as function of temperature, is reached about 30 degrees. However, this is not a general rule for all the plants, and some species will suffer losss of efficiency at such temperature. Nonetheless, this is shown here:
X-axis is time, and Y-axis is photosynthesis rate. As you can see, maximum rates are achieved at higher temperatures, but after some time, thermal stress damages the capability of the plants to do photosynthesis and rate falls. Most stable values are reached at 25 degrees, and at 30 degrees, but even at 30 degrees some degradation is observed within the time.
The important point of this is that CO2 consumption changes. In fact, activity doubles every 5 degrees of change. This means that having an aquarium with certain dosage of CO2 at 25 degrees, and having a sudden change to 30 degrees, CO2 consumption will significantly increase. If CO2 injection is not accordingly adjusted, then some loss of balance between CO2, light, and nutrients is observed, what can drive towards appearance of algae, overall if the temperature remians high for long enough time (i.e. several days).
So when goes to temperature, the main effect is related to the metabolisms of the plants and not to the physical properties of CO2. There is some confussion around about this topic, but I hope to clarify this now.
You can read more about it here:
http://www.thelivingtank.co.uk/2016/08/article-co2-q-science-behind.html
Hope this help.
Cheers,
Manuel