Diatoms discussion

[papa_c]

Here’s a diatoms question for discussion.

My tank has been stable for some months and plant growth great, no signs of diatoms at all. Maintenance, EI dosing, CO2 has stay constant, no changes to anything.

This week I have had an outbreak of diatoms on dwarf hair grass, the only change is the ambient temperature this week with the mini heatwave experienced.

With the increase in water temperature this would affect the solubility of CO2 in the water could this cause the outbreak?

 

[kadoxu]

It could be... if CO2 becomes the plant growth limiting factor, the plants could be taking a lower amount of nutrients from the water, leaving the extra for algae to feast on.

 

[Manuel Arias]

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

 

[kadoxu]

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.

Will the photosynthesis rate come back up during a 7 hour cycle? or does it keep going down and recover at lights out?

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 does this mean that we should increase the CO2 injection to keep up with demand when the temperature rises?

 

[Manuel Arias]

So does this mean that we should increase the CO2 injection to keep up with demand when the temperature rises?

Yes, if you expect to have a few days with higher temperatures. Obviously, this is a general rule and as such, it is not always valid. For instance, having low demanding plants involves they will consume more CO2 but again, low-demanding means they use low amounts, so even if they increase the rate, the values will still low. This is also true for low dense/ high dense planted tanks. I would not change it, however, if the period of heat is expected to be short.

But in general terms, a standard planted tank with substantial amount of plants, should be adjusted to receive more CO2 when temperature in the water goes over the standard (or normal for that tank) temperature, that's right.

Cheers,
Manuel

 

[kadoxu]

Sorry, didn't expect you to be so fast answering and added another question to my post...

 

[Manuel Arias]

There is an errata in my former message. Enzymatic rate doubles every 10 degrees, not 5. This means that 5 degrees involves about 50% more consumption, not double. I will reapond to your other questions later.

Cheers,
Manuel

Enviado desde mi C6903 mediante Tapatalk

 

[Manuel Arias]

Will the photosynthesis rate come back up during a 7 hour cycle? or does it keep going down and recover at lights out?

Photosynthesis rate relies in several factors, mainly light intensity, CO2 availability, temperature, and of course, nutrients. However, each demand happens at different level. For instance, CO2 is not used unless there is previously some energy coming from the photosystems allowing to combine it with water to assimilate the carbon and then releasing oxygen. Because of that, photosynthesis cycle is controlled by light. No light, no photosynthesis and temperature will not have effect into this. Now, loss of photosynthesis rate due to heat is due to a different matter. Enzymes are mainly proteins, which means they are stable only within a given range of temperatures. The loss of photosynthesis rate is due to the damaged cause bu excess of temperature over the enzymes. As result of that, enzymes concentration diminishes and capability to perform photosynthesis is also reduced. Now, getting down the light does not stop to the enzymes taking thermal damage as far as the temperature is high. This happens despite of the enzyme being used or not. Because of that, when you shut down the lights and you wait your seven hours or whatever time, and you turn on the light, the photosynthesis rate will be lower than expected because the damaged enzymes will have not been recovered. The proper recovery would not happen until temperature gets down, what means that persisting high temperature can actually kill some species of plants. And the same is true for animals.

I think this is what you were asking, but if not, please, let me know.

Cheers,
Manuel

 

[kadoxu]

I think this is what you were asking, but if not, please, let me know.

Yup, that covers all of it.

I just wanted to be sure about what would happen when temperatures kept at, let's say, 40º, if it could go up and down with larger time intervals, but it makes sense that the photosynthesis rate would keep going down and the plant eventually dies.

Not that I want to keep plants at 40º... I was just curious!

Thanks!