14 ppm CO2 proven detrimental for freshwater tropical fish

In my study, I stumbled upon an interesting article that examined the effect of elevated CO2 concentration (14 ppm) on freshwater tropical fish Mozambique tilapia (https://en.wikipedia.org/wiki/Mozambique_tilapia).


The study's highlights:


1) Elevated CO2 (as well as temperature) levels have a negative effect on hematological parameters.


"As a result of elevated carbon dioxide concentration in the water, hypercapnia is observed due to abnormally high level carbon dioxide in the blood. The increase in blood partial carbon dioxide pressure can cause a respiratory acidosis in fish. Because increased carbon dioxide concentrations cause acidification in the blood and tissue respiratory pigment, it causes a reduction in oxygen intake and delivery. In cases where acidification occur and blood pH fall, fish can compensate the reduced red blood cell pH with Na+/H+ ion exchange by catecholamine proteins. Althought the fish in our experiment exposed to elevated CO2 levels were able to solve the above mentioned problems (with the help of adaptive mechanisms), and the hematological parameters returned to the normal values at the end of trial, it should not be inferred that the fish health is not adversely affected."


2) At elevated levels of CO2 there was an inhibition of activity of enzymes that control the transmission of sodium-potassium ions in cells (i.e. sodium-potassium pump aka Na+/K+ ATPase) within two weeks.


3) For the fish to survive it was trying to cope with these adverse conditions using a variety of adaptive mechanisms.


In the study, any death case was observed neither in control nor in test group fish. Furthermore, no change was observed in feeding and behaviors of fish in any group.


Source: http://www.sciencedirect.com/science/article/pii/S1382668916300965


For discussion: It's interesting that although no fish died at an elevated level of 14 ppm CO2, and all the fish seem to have behaved quite normally, hidden from our eyes a certain negative internal changes occurred in the fish. And although the fish managed to overcome it, it does not mean that the elevated CO2 levels would be a "cakewalk" for the fish (as the study shows). Even under only 14 ppm CO2 the adaptation mechanisms had to have a pretty hard time to be able to eliminate the excess CO2 in the blood. There was used a total of 144 pcs of fish in the experiment weighing 13-15 g each, which should correspond to a length of about 3.5 to 3.7 inches (these were probably a relatively young fish).


Often I here an argument saying that "my fish are not dying on any carbon dioxide poisoning, and are behaving perfectly normally and are breeding ... which apparently proves that the elevated CO2 levels have no negative effect on aquarium fish." However, this study highlights the negative consequences that are not even visible to the naked eye, so many aquarist often do not notice them (even if they are watching their fish very carefully). So is it really necessary and considerate to fish to use such a high levels of CO2 in planted tanks? I liked one article, in this context, that I had come across in one old magazine where the author says, "The optimal amount of [CO2], which is beneficial to plants and is not detrimental to fish, is in the range of 5-10 ppm" (B. Huschina, Mysterious carbon dioxide, Aquarium terrarium, 1984, Vol. 27, No. 3). And now one heretical question: Would not be better to reject the everywhere-recommended-level of 30 ppm CO2 (or even more), and return back to these values?

 

Let me address your objections one by one:

The fish in the study were about 3.5" long.

Citation from the paper: "In the study, ... no change was observed in feeding and behaviors of fish in any group."


My comment in the previous post: "This study highlights the negative consequences that are not even visible to the naked eye, so many aquarist often do not notice them (even if they are watching their fish very carefully)".


So, if Discus starts acting weird (= visible negative symptomps), then its adaptive mechanisms are already failing to eliminate high CO2 levels in its blood. This is a clear proof that the invisible (inner) negative effects occur under much lower CO2 levels than 45 ppm. At 45 ppm the negative effects are so serious already that they already affect the outer behaviour. The whole study is about the inner negative effects (that you can't see or notice). BTW, as I recall, you have mentioned elsewhere that you are using 50-70 ppm CO2 in your main tank, aren't you?

That's a good note. This can help in some situations ... if the degassing is effective enough overnight. But you should also note that many folks add CO2 24/7.

According to my experiences, many folks don't manage CO2 very well, so it's not uncommon their CO2 levels are increasing during the photoperiod from say 30 ppm up to about 80 (even more) CO2. There was one article about CO2 behaviour during the day, but it's not available anymore. It showed how easily CO2 increases to very dangerous levels if you don't use enough aeration in your tank to level it up. But in case you use 50-70 ppm in your tank (although for only about 1/3 of a day) ... that's 4-5x higher than the level investigated in the study. I think some fish species may have a really hard time adapting to these levels. Some of them may even have a lower breeding rate or higher egg mortality, maybe a shorter lifespan also ... who knows. There may be a lot of invisible negative effects going on with some of your fish/shrimps.

Again, they may seem to do very well, but this does not mean their adaptive mechanisms are not having hard time to eliminate high CO2 levels in their blood. As you probably know not all negative effects may have a visible manifestation. I have read about nephrocalcinosis with the respect of elevated levels of CO2 also, which can be found only by autopsy.

I can't comment on this finding as I don't know any details. Were there any fish living? Were they studied? ... and what parameters were investigated? What was the results? Is there any paper available about this research/experiment that will show the effects of such an elevated CO2 levels on fish?

Again, I can't comment on this, but even if ADA claims prove to be wrong, this does not mean that the study's conclusions are wrong as well, does it?

How should I understand this argument? Do you want to say that if there is a huge band of people using elevated CO2 levels it proves it is not detrimental? In 1970's or 1990's some studies were not available, so the people could hardly know about any invisible negative impact of elevated CO2 levels on their fish. Again, we speak here about the invisible negative effects that can't be seen by a naked eye.

In nature, the light intensity is about 1500-2000 µmol PAR under the direct sunlight. Still, the average CO2 level in the Amazonia river and its tributaries is 6-8* ppm CO2.


* see MCCLAIN, Michael E, Jeffrey Edward RICHEY a Reynaldo L VICTORIA. The biogeochemistry of the Amazon Basin. New York: Oxford University Press, 2001. ISBN 0-19-511431-0.


According to Dr. Ole Pedersen from University of Copenhagen, "Natural waters vary tremendously in CO2 concentration but contrary to what most people think, most water bodies are supersaturated with CO2, i.e. concentrations above air equilibrium which is typically around 10-20 µM (0.4-0.8 ppm) depending on temperature and salinity. Nevertheless, lakes in general have lower CO2 concentrations than streams, and the smaller the stream, the higher the CO2. Groundwater can have anything between 1000 and 2000 µM (40-80 ppm), streams from 1000 (4.4 ppm) to below 10 (0.4 ppm) (the latter would be the lower reaches of Donau or Rhine) and lakes between 200 (8.8 ppm) and below 1 (0.04 ppm) ...".


So, levels above 40 ppm are common for groundwaters rather than streams. So, in nature most of the aquatic plants grow under much lower levels of CO2 than we often recommend (30 ppm), and this furthermore often under full sunlight (~1500 µmol PAR). Even under an undirect light the irradiation can reach 500-600 µmol PAR. In short, much lower CO2 levels vs. much higher light intensity (much more than PCL or MHL) in nature.

Before someone shows/proves me how detrimental elevated CO2 levels can be, I would be probably also fine with my subjective observation. But once I found that there are any negative effects going probably on in my fish, I would like to adjust my attitude accordingly. I don't want to ignore the risks.

Agree, fish can vary in their response to elevated CO2 levels. The same applies to plants. Different plant species have different demands to nutrients, different threshold for toxicity, use different physiological/adaptive mechanisms. But it is a good and reasonable habit to adjust our methods according to the most demanding/sensitive species.

I have a planted tank with fish. I like the plants, but I want to be considerate of my fish also. With respect to my plants I would like to supply them with a reasonable deal of nutrients (incl. CO2), but with respect to fish I would like to keep it as low as possible. So the result must be some kind of compromise (with respect to plants as well as critters). I think you should understand this approach.

You should differenciate between plants preferences vs fish preferences here. Of course, under higher CO2 levels the plant growth will increase also (and the overall condition may be even better, because under higher growth rates less algae can probably attach to their leaves, etc.). But first, I don't want to have a plant farm in my tank. I don't sell plants as you, so I don't need nor want to trim them each couple of weeks, nor have always enough time for demanding maintenance (one that is needed when you go full-speed). Second, I focus not only on the plants, but on my fish also, and I want they have the best possible conditions in my planted tank. You repeat your argument about "fish still breed" over and over. The whole point of the above study is to point out that there are some negative effects going on inside our fish ... unnoticed to hobbyists, not visible to our naked eyes. Still, they are there and are real. I don't want to persude you to pay attention to it. You have chosed to ignore it, I have chosen to pay attention to it, and adjust my method accordingly. No need to fight over it.

There should not be any "plants vs fish" approach IMO. As I said, I have a planted tank (not for any contest reasons, but just for my joy and education) with fish inside. Thus, my main concern is to provide the plants as well as fish the best environment (conditions) I can. When I found that plants have some demands (like strong light, enough levels of essential nutrients, flow, temperature, absence of toxic elements/compounds, etc.), I will do my best to ensure they have all they need for a good growth. In the same way, when I found that fish have some demands (like lower light, clear water with minimum level of impurities [incl. low CO2], flow, temperature, absence of foxic elements/compounds, etc.), I will do my best to ensure they have all they need for a good living. If some of these demands go against each other (i.e. plants want more CO2 vs. fish want less CO2), I will try to find out some reasonable compromise. In the respect of CO2, ~10 ppm seems to me as a good compromise. Under this level most plants should grow exceptionally well, while most fish should be probably fine (with low and well-manageable level of negative effects).

 

ad 1) No, my name is Jiri N.


ad 2) In a similar way I can describe my failures with trying to grow plants under EI. Would you conclude from this that EI is not working? Each method will work under some circumstances. As you probably noticed, basically I agree that under higher CO2 levels (higher that the suggested 10 ppm) the plants will grow probably a little better. The higher growth rate may function as one of the factors protecting plants from algae attachment, and more acidic water can inhibit the growth of some kinds of algae. I do not question the plant health or growth rate under higher CO2 levels (10+ ppm). I just share my doubts about the health of our fish under elevated CO2 levels based on the recent (2016) research. As I have already pointed out plants demands may sometimes go against the fish demands (especially in water quality, incl. CO2 concentration). So I understand how higher CO2 levels may be beneficial to plants, but in the same way we should understand how higher CO2 levels may be detrimental to fish, shouldn't we?


ad 3) I see a difference between low tech tank withouth CO2 and low light vs. high tech tank with 10 ppm CO2 and high light. I am working on a good documentation for these kind of tanks, because I know that you probably won't believe me anyway if I would just tell you that "it works". I was using EI for many years, and was able to grow successfully many plants (incl. Alternanthera reineckii), but I am aware of its limits. It can work, but only under some circumstances. That's why I have no problem to believe Tom is growing many plants just fine in his EI tank. But it has some limits. Under different circumstances, it can be a disaster (for whatever reason). I think it is good to know these limits.


Fablau, what's wrong on sharing one scientific article with others? I think it presents quite interesting findings. Should we just ignore it only because it does not fit into our concept? Also, I don't persuade anyone to change his method. You can use whatever CO2 levels in your tank. It seems like if one presents here an information that seems to be somehow in conflict with EI, he is immediately treated as if he was trying to put Tom or EI down. But such an attitude is just paranoic. I think that it is good and desirable to adjust our concepts in the light of recent research, experiences or knowledge.

 

~7 ppm O2 under 25°C


1) Using Google you would find a link to the fulltext on ResearchGate (you need to be registered there for access, but it's for free): https://www.researchgate.net/publication/301829296_The_effects_of_elevated_carbon_dioxide_and_temperature_levels_on_tilapia_Oreochromis_mossambicus_Respiratory_enzymes_blood_pH_and_hematological_parameters


2) Using an online "oxygen saturation calculator" (http://www.hbuehrer.ch/Rechner/O2satur.html) you would find that ~7 ppm O2 under 25°C means about 90% saturation (which is quite high).