# Understanding CO2/pH levels



## Bacms (20 Oct 2015)

Hello everyone,

I have started my first planted tank about a month ago and I am still struggling with algae. First it was diatoms now blue/green algae and some filaments of green algae. So I have decided to take action and buy a pH probe. Most people say I should aim to a 1 pH unit drop, which looking at the CO2/pH/Kh table makes sense. 

The problem I have been having is that to get a full unit drop my CO2 drop checker is way into yellow and I am worried I will asphyxiate any critter I will introduce. 

My missus have been at home this week and I have asked her to keep measuring the pH during the day. This is the results I have got for the last 2 days:

before bed pH measurement -> 7.2
before CO2 on (6am)-> 7.2/7.3
Lights on (10am)-> 6.8(lime green drop checker)
11:47 am -> 6.7 (yellow drop checker)
13:02 -> 6.6
13:53 -> 6.4/6.5
14:00 CO2 off -> No measurement 
16:00 (Lights off) -> 6.7

Reduced CO2 and light to try and prevent the drop during day to make it safe for the 6 ottos I introduce yesterday so wanted to be sure I didn't kill them.

before bed pH measurement -> 7.4
6am (CO2 on) -> NA
8am -> 6.9
9am -> 6.8
10am -> 6.8/6.7 (Lime green drop checker)
11am -> 6.7
12am -> 6.5
13:00 -> 6.7 (probably a bad measurement)
14:00 (CO2 off)-> 6.3
16:00 Lights off ->  6.8

Based on these readings I am not even close to get 1unit of drop by lights on but the pH continues dropping during the photoperiod so I would assume I need to lower the bubble rate and start earlier, but my main problem is that I already have a yellow drop checker and don't want to kill the ottos and most certainly don't want to kill the amano shrimp when I add them later this week. 

BTW distribution is via in-line diffuser with a spray bar. I can see bubbles all around the tank lower in the corners and substrate level which is where the drop checker is placed. Also ottos seem to not care at all during today light period even with the drop checker on yellow but I am worried this may have long term effects. 

So question is what am I doing wrong? I also use a sodastream bottle in about 2 weeks so I am injecting quite a lot of CO2.


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## 5678 (20 Oct 2015)

I don't profess to be an expert on this but I had similar issues. I'll list what I changed to address them. 

- Run co2 24/7, yes it may waste gas. But it meant I could get a stable level. 
- Move to a "good" in tank diffuser. I tried some cheaper ones, still had co2 deficiency symptoms. Am now using an ADA one and it makes a massive difference. 
- I was also using a lot of gas with the inline diffuser. Since using my current setup I am using less gas. I can only conclude the inline diffuser was inefficient. People state the opposite I know. This is what I have seen for myself though.


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## ian_m (20 Oct 2015)

I use about 15gr CO2 per day on my 180litre tank, so 2Kg CO2 lasting about 100-120days, with a green/yellow drop checker. So about 1gr CO2 per 10litres of tank water per day. A Sodastream bottle is 420gr.

You need to move your drop checker around the tank, I was really surprised I could get yellow drop checker in one place and blue in another (and associated algae). Improving flow and distribution fixed this.


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## Bacms (20 Oct 2015)

I also have a 180L and the consumption was the same for tank diffuser or inline. I am still not convinced I am not injecting CO2 I just took some water out in a cup and will let that rise equilibrium with air CO2 so I can have a better sense of how much the pH is dropping as it does not make sense to me I should expect a 1 unit drop if I don't know how much CO2 is in there already. 

In all the places I have tried including the ones with plants doing badly the drop checker was still yellow. 

What I am worried is finding the ottos dead without realising I am gassing them. Is there any other symptoms apart from them gasping at the surface? And do shrimps show any symptoms? 

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## Jose (21 Oct 2015)

Your CO2 must be off and degassed before you introduce any new critters to the tank. Shrimp will act strange i.e move too much and violently aorund if co2 is too high.


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## 5678 (21 Oct 2015)

Jose said:


> Your CO2 must be off and degassed before you introduce any new critters to the tank. Shrimp will act strange i.e move too much and violently aorund if co2 is too high.


Is that a common approach? I tend to drip acclimatise anything over a few hours with my co2 on and that seems ok so far?


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## Jose (21 Oct 2015)

5678 said:


> Is that a common approach? I tend to drip acclimatise anything over a few hours with my co2 on and that seems ok so far?



That only means your co2 is not very high. As you drip your water the co2 will just "evaporate" from it. Now, when you throw your fish into the tank from the holding container which supposedly has the same water then you're in big trouble. It's happened to hundreds of people including myself. Learn from our mistakes.
Also having CO2 on 24/7 is not a great idea. People who do this simply have lower levels of CO2, so lower light as well. CO2 is always going to cause some stress to the fish. So no CO2 at night means they can recover and rest.

Another thing is your Drop checker will detect all the CO2 in your tank and not only the dissolved co2 which is the one that stresses fish the most. This is why you think you have huge ammount of co2 whilst it might not be that much. A good test is to measure the pH in your tank without CO2 and then once again when co2 is on (after some hours). The difference between the two values will tell more about your real co2 ppm.


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## Bacms (21 Oct 2015)

Hi Jose I normally introduce them in the evening when the CO2 is off and then they will have 4h on the morning after to start acclimatizing. 

I am using the pH method and that for me is what is not making sense at the moment. I start CO2 4h before lights on, pH drops from around 7.3/7.4 to about 6.8. This is enough to change my drop checker from dark green to lime green. But then it continues to drop all the way down to 6.4/6.3 at which point the drop checker is on yellow for a couple of hours already. So it seem 6.8 should be the point where CO2 is close to 30ppm but that is only a 0.6 drop on the pH. Not the 1 unit people recommend. Maybe the forum should start to have a "fly in Clive" to correct all the problems with out tanks


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## Jose (21 Oct 2015)

Bacms said:


> Hi Jose I normally introduce them in the evening when the CO2 is off and then they will have 4h on the morning after to start acclimatizing.


Thats good, as long as you dont introduce them with a lot of CO2 in the tank water.



Bacms said:


> I am using the pH method and that for me is what is not making sense at the moment. I start CO2 4h before lights on, pH drops from around 7.3/7.4 to about 6.8. This is enough to change my drop checker from dark green to lime green. But then it continues to drop all the way down to 6.4/6.3 at which point the drop checker is on yellow for a couple of hours already. So it seem 6.8 should be the point where CO2 is close to 30ppm but that is only a 0.6 drop on the pH. Not the 1 unit people recommend. Maybe the forum should start to have a "fly in Clive" to correct all the problems with out tanks



Now this is a big heated debate. What is more accurate DC or ph drop? Well I can tell you what I think and I've tried both. I really hate dropcheckers, because of a few things I wont get into now. But, if you prepare your own 4dkh solution, have good flow in your tank and dont have CO2 bubbles travelling inside it, then a d.c. might give some sort of reasonable reading. But still it will be a reading of a few hours earlier and it's very hard to know the exact shade of colour its got.
Now with a ph pen. This is what I use and wouldn't bother with anything else. Its been shown that a a bit over a 1 unit ph drop is equivalent to 30ppm of co2. Its doesnt matter what hardness your water is. In practical terms in almost any water this will be true, specially if you're doing water changes every week. Now this method can't be used without care. You need to sort of "calibrate it" and use it as a guide.
Something even more important is surface agitation of the tank water. Its hard to keep a constant co2 ppm in the tank, so you need to have good and constant offgassing of co2, otherwise co2 levels just keep climbing.

So in practical terms I would do as follows.If you want to add more co2 (for whichever reason) then adjust your surface ripple first. So, some surface movement which needs to be constant. And you shouldn't have surface scum or this will trap more co2 making it to build up in the tank.
Then measure what pH drop you get. pH should stabilize at a certain value after some hours which means co2 in the tank is staying constant. Ideally your ph should drop before lights on and stay at the lowest value during the whole of the photoperiod. This is ideally, so many will say you dont need it.
Now, decide if you want more co2 and open your needle valve just a tiny tiny bit.
Then look at critters in the tank for response and measure ph drop again. Repeat this over and over until you're happy with the co2 levels, but give it time (days even) in between the changes. I am afraid there is no easy way to sort out the co2 factor.

Another option is sticking with a safe co2 level like the one you have and tweak the ammount of light as to not get any plant health issues. Because every plant is different. So you might be fine with thos co2 levels, medium light, and easier plants.


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## Bacms (22 Oct 2015)

Thank you for the lengthy reply Jose I will observe the shrimps with detail on Saturday to make sure the CO2 is not too high.

The water I took to a cup and left out of the tank for 24h had a pH of 8.2 so if I take that as the reference for being in equilibrium with the atmosphere then it would make sense drop checker becoming yellow at around 6.9/6.8

What I found strange is that after 8h with the spray bar raised I can only make the pH raise to 7.4 which I was assuming was the equilibrium point. But unless there is any strange factor causing the pH to raise massively on the cup then that should really the real value. Or am I missing something?


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## ian_m (22 Oct 2015)

Try turning off and unplugging all your tank electrics before taking a tank reading. Some people have seen pH rise by over a unit when their electrics are off. To do with leakage currents in the water affecting the pH reading.


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## X3NiTH (22 Oct 2015)

You're not missing anything, your current spray bar configuration doesn't produce enough gas exchange at the surface to allow the tank to fully degas co2 to reach equilibrium with the atmosphere at the same rate as the sample in the cup. 

What Jose said about surface scum is important because if there is any it will cause major issues not only with trapping co2 but also blocking O2 from exchanging with the atmosphere, the more the scum builds up (it's not always readily apparent) the less co2 gas the fish can tolerate due to lack of O2, this can cause confusion because you find yourself dialling down the gas when the DC says it's fine for the plants, this can be less of an issue if there are lots of plants pearling through photosynthesis boosting the waters O2 content but if for any reason the plants don't produce enough O2 say due to lack of a fert then there will be a deficit of O2 overnight and next day you find fish at the surface at a higher ph than the day before, causing you to dial the gas down further which starves the plants even more again reducing O2 output (In a fish less planted environment this will eventually cause plants to suffocate and self destruct).

Using an airstone during lights out and before gas on will help to degas co2 further towards the equilibrium you saw in the cup, (not essential to fully degas co2 to equilibrium just enough that it's not an asphyxiation issue combined with plant co2 output during dark period) the more co2 you degas overnight may require you to put the gas on earlier to compensate for how much more gas you need to inject to have a green DC for lights on (or at least going green within an hour of lights on due to the lag the DC has in comparison to a measured ph drop). Using an airstone overnight has the added benefit of fractionating any scum on the surface and causing it to mix and clump together within the water column where it can be caught by the filter, unfortunately running an air stone during the day to reduce surface scum will require extra co2 to be injected to offset the higher rate of gas exchange.

Shrimp will faint under high co2, they will also climb out the tank if they can. An unconscious shrimp is fair game to any fish that can fit at least a leg in its mouth.

Fish gills will redden and gape more just before the fish head to the surface under higher co2 conditions, you are more likely to observe fish at the surface than notice gill appearance for signs of discomfort, adding air through an airstone temporarily will help off gas a little more co2 giving the fish a little more breathing room giving you time to adjust the gas down.

The more O2 you can get in the tank the higher concentration of co2 fish can tolerate.


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## Jose (22 Oct 2015)

Yes your ph values do make sense, as explained by others.


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## Bacms (22 Oct 2015)

I do clean surface scum at water changes and I did notice it was getting bad but I just cleaned it again and did a small water change about 25% in preparation for tomorrow. 

But if the pH is real than I need to lower my CO2 right? I don't notice the fish gasping at the surface maybe more red on the gills but hard to say as they always have them reddish anyway. 



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## Jose (23 Oct 2015)

No need to lower co2 really. Maybe more surface movement.


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## Manuel Arias (23 Oct 2015)

X3NiTH said:


> The more O2 you can get in the tank the higher concentration of co2 fish can tolerate.



Sorry but this is incorrect. The CO2 and the O2 are not in competence in the water, and they have different effect in fishes when goes to concentrations in the water. The real problem to breath is related to exchange of gases between the body of the organisms and the water. In fact, it is the same for terrestrial organisms, anyway. There is a need of releasing the CO2 from the body to the air/water, which is only possible if exists certain gradient of concentrations between body and external environment. In aquariums this means that if the amount of CO2 gets a maximum value, the fishes are not able to release the CO2 in their bodies and then die. With the O2 the problem is similar: There is a need of O2 being in such a concentration that the flow of this gas towards the body of the organisms is enough to cover their needs and produce energy. 
It is totally possible to suffocate organisms in water totally saturated of O2 if the levels of CO2 are high enough. In fact, this is the classic problem of relationship of pH/kH and CO2 levels in water, as even if your plants are bubbling (symptom of O2 saturation in water) you can have levels of CO2 big enough to avoid the exchange of CO2 through the gills, and then killing the fishes.

The use of the airstone obeys a different purpose that many times we forget: The plants also breath and use oxygen. It is the way in which they also generate energy in their metabolisms. Photosynthesis is only a catalytic process to create basic molecules the plants can use later to build more complex molecules like proteins, fats, vitamines, etc. The plants breath during the day and night. However, during the day, the balance of use of O2 is positive, and then, they free O2 to the water. But during the night it is not the case, and the plants are in-taking O2 for their metabolism. If you had been saturating the water with CO2 during the light hours, when you turn them off, the plants stop generating O2 but still breathing, which can kill the fishes by lack of oxygen or saturation of CO2. Surface turbulence and/or airstone helps to avoid the problem, by injecting O2 into the tank, in one side, and favouring the removal of CO2, in the other side. The bubbles of O2 generated by airstone have a very big surface in relationship to the volume of the bubble, which allows the exchange of O2 and CO2 through the limit layer of contact. In other words: in each thin bubble generated by the aireation, the excess of CO2 of the water is moved to the bubble, and the lack of O2 is extracted from the bubble, which ensures to have the right gas balances in your water. That is why night aireation can make a difference also in the growing of the plants, as you ensure that they also have enough O2 to do their metabolism during the nights.

The easiest way to monitor this is by checking the pH during several moments of the day, and you will see the curvature caused by the flows of CO2.


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## X3NiTH (23 Oct 2015)

Oops, lost in translation.



X3NiTH said:


> The more O2 you can get in the tank the higher concentration of co2 fish can tolerate.





Manuel Arias said:


> Sorry but this is incorrect.



Taken out of context from my post and smashing it with science, you are quite correct. However I was talking more generally in relation to my post on surface scum effects previously mentioned by Jose and I really should have been clearer and preceeded my statement with "In an oxygen depleting system" to keep it more in context and also added that "once oxygen depletes from the system it's not coming back readily through surface scum".


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## Manuel Arias (23 Oct 2015)

X3NiTH said:


> "In an oxygen depleting system" to keep it more in context and also added that "once oxygen depletes from the system it's not coming back readily through surface scum".



Good point and clarification.   In any case, I would say that smashing it with science would involve putting here equilibrium equations and references to papers... 

But you are right at some point as any scum or superficial layer will reduce the exchange of gases with the atmosphere, for sure, so an airstone will also mitigate part of this problem by adding oxygen to the tank and breaking the scum layer. I also spoke in general terms, but  they remain valid under your comments. Suffocation can come from two problems that usually go together but not necessarily: The build up of CO2 in the water, so the fishes cannot get rid of the CO2 inside their bodies, or by a lack of oxygen so the fishes cannot breath at the levels they need for their metabolism. The scum impacts in both of them, but the tolerance of fishes to CO2 is not at all related to the levels of O2 in water. In other words: If the CO2 accumulates in water until deadly levels, injecting more oxygen will not avoid the problem, as what is really requested is the aireation or ventilation of the water to reduce the CO2 levels. On the other hand, very low levels of CO2 will not help at all if the fishes are under low levels of O2, so fishes can also suffocate under 0 ppm of CO2 in water if the O2 levels are not at a minimum value required for the livestock.


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## Jose (24 Oct 2015)

The more o2 there is in the water the higher co2 concentration you can keep without fish issues.
There are many more things to consider as well but this statement is true. It doesnt mean there is no limit to how much co2 you can inject obviously.


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## zozo (24 Oct 2015)

ian_m said:


> Some people have seen pH rise by over a unit when their electrics are off. To do with leakage currents in the water affecting the pH reading.



I did have some eratic readings on the Milwauke with even sticking my finger in the tank or something metal.. I noticed because it's a controler and it started clicking. since i'm keeping a constant eye on it, if anything electrical comes near the probe it reacts, like my vacumer is driven by a small 12 volt airpump i mounted to the vacumer. The Milwaukkee is very sensitive.. The PH probe works as e regular voltage meter and compares conductivity deferential between known conductivety of the solution in the probe and this of the tank water. This difference is recalculated to a PH number.. 

The Hanna works with an other methode it uses a Anode/cathode measurment, this is a much more stable reading than just the single probe measuring without the anode pin. What ever i do or try the Hanna stays stable, while the milwaukee goes nuts..

If you have a pocket meter you can look and if you see a small metal pin next to the glass probe than it's an anode/cathode device. The meters without the metal pin, is not yet totaly clear to me what the difference in measurment is but it's more susceptible to interfearnce, it probably searches for another negative or positive i guess it searches for ground. so if this other comes near, the dancing around occurs..


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## Manuel Arias (24 Oct 2015)

Jose said:


> The more o2 there is in the water the higher co2 concentration you can keep without fish issues.
> There are many more things to consider as well but this statement is true. It doesnt mean there is no limit to how much co2 you can inject obviously.



Out of curiosity, which is the argument for this? I mean, if you can extend your point, as it is interesting, and I might be wrong. F

For many years in fish physiology has been stated that breath in fishes is not linked to the relative concentrations of O2 and CO2, unless CO2 concentrations in water are big enough to block the exchange of CO2 from the blood of the fishes with O2 in the water, or the O2 concentrations are not enough to cover the needs of the fishes. Meanwhile the CO2 levels in water are allowing the excretion of CO2 through the gills , the fishes have adaptations (until some point) to make available the oxygen in the water by increasing the ventilation rate and the cardiovascular activity to compensate the lower rate of exchange of CO2 due to the higher concentrations in the water. The intake of O2 is then driven by the Bohr-Haldane effect as result of the pH changes in blood due to this CO2 transfer. Meanwhile the O2 levels are suitable for the fishes needs (this level is independent of the CO2 levels in water), they have mechanisms to handle the higher levels of CO2 until the point in which the stress caused by the reduction of the gradient of concentrations overwhelms the capacity of the fish to compensate it by other means. As it is this gradient who controls the exchange rate of gases, does not matter if you increase the O2 concentrations in water, as then the fish will not be able to use that available oxygen because cannot remove the CO2 from the hemoglobin in the blood, and then suffocating.

The following figure explain this: 




 

As you can see, it is the relative concentrations of CO2 between body and water what enables the breathing. If the CO2 levels in water are high enough, the gradient indicated in point (4) of the figure is much lower, difficulting the gas transfer. In fact, this gas transfer involving the change of the pH in the blood is what allows to the organism to grasp O2 from the water, via Bohr-Aldane effect, so regardless of the O2 concentration very high in the water, if the CO2 levels in the environment are high the mechanism is not possible.

It has been stated, however, that higher levels of O2 are positive for fishes, meanwhile the CO2 levels are on bay in specific ranges, but the reason for that relies in receptors of the gill´s cells that activate specific patterns of behaviour and physiologic reactions in the fishes. In other words: when the conditions are good the fish relax and suffer less stress. However, as mentioned, this only happen in specific ranges of relative concentrations of CO2 and O2 in water, and there is no general relationship between a better tolerance to CO2 by increasing O2 levels, as the mechanism allowing the breathing is the differences of concentration in CO2 between the blood and the water in a given temperature. In last years some people are publishing about the role of the pH of the environment in the mechanism of gas exchanges between gills and water, but they only point out in the direction that lower pH in the water can reduce the tolerance of fishes to CO2 levels, and not totally related to this discussion.

You can read abut the fishes adaptations and responses to high CO2 concentrations in water in the following paper, which also explains the role of the differences in the partial pressure of CO2 in environment and fishes and its effects:

http://onlinelibrary.wiley.com/doi/10.1029/2004JC002564/pdf

And a good reading about the Bohr-Haldane effect is found here, where you can se that the release of CO2 to the water is what triggers the O2 intake:

http://brauner-home.zoology.ubc.ca/...l-Interaction-between-O2-and-CO2-exchange.pdf

Well, now we smashed it with science.  But I think we should move back to the topic of this thread, anyway.


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## Jose (24 Oct 2015)

Maybe more oxygen makes the whole process of CO2 transport/excretion more effective as compared to low o2.


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## ceg4048 (24 Oct 2015)

Manuel Arias said:


> Out of curiosity, which is the argument for this?


The argument is thus (it is clearly explained in your figure 5.8):

At low pH, Hemoglobin's affinity for Oxygen is poor and it's affinity for CO2 is high.
At high pH, Hemoglobin's affinity for Oxygen is high and it's affinity for CO2 is low.

This mechanism is by design. When the red blood cells are in close proximity to the tissues, the pH is low due to the tissues excretion of CO2. The Hemoglobin then drops it's payload of Oxygen and attracts the CO2 molecules. The blood cells then travel to the gills where the pH is normally higher they drop their payload of CO2 and attract the Oxygen molecules for the return trip to the tissues.

When the ambient water has a high partial pressure of CO2 it blocks the ability of the the bloodstream CO2 to diffuse through the gills to the water. This keeps the CO2 in bloodstream solution and causes a drop in blood pH. The cardovascular system combats the bloodstream acidity by releasing bicarbonate to buffer the acidity, however, the Hemoglobin's affinity never recovers to 100%. Typically, it can only achieve a maximum of about 96% of the pre-buffered affinity, and can be even lower depending on the pH and the buffering ability of the fish. Therefore, a higher Oxygen content in the water column can make up, to some extent, the loss of Hemoglobin-Oxygen affinity.

In our case, effective CO2 distribution and uptake by plants allows a higher rate of photosynthesis, which generates a higher Oxygen ejection  into the water column. So it helps to some extent but as Jose mentions, cannot overcome all higher levels of CO2.

Cheers,


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## Manuel Arias (24 Oct 2015)

ceg4048 said:


> So it helps to some extent but as Jose mentions, cannot overcome all higher levels of CO2




Hi ceg4048,

This is the key mark: "At some extend", which is only valid to a reduced range of CO2 concentrations, as explained before, and also explained in one of the papers I put, sorry.



ceg4048 said:


> When the ambient water has a high partial pressure of CO2 it blocks the ability of the the bloodstream CO2 to diffuse through the gills to the water. This keeps the CO2 in bloodstream solution and causes a drop in blood pH. The cardovascular system combats the bloodstream acidity by releasing bicarbonate to buffer the acidity, however, the Hemoglobin's affinity never recovers to 100%. Typically, it can only achieve a maximum of about 96% of the pre-buffered affinity, and can be even lower depending on the pH and the buffering ability of the fish. Therefore, a higher Oxygen content in the water column can make up, to some extent, the loss of Hemoglobin-Oxygen affinity.



Here, you are just reasoning in the same way I did, but with one mistake: The mechanism I put in the figure is incomplete, and then, your conclusions are wrong. The complete process involves both Bohr and Haldane effect. As you say, the carboxilasa enzyma plays the role to compensate the CO2 productions by generating carbonates to regulate the pH in blood, so you are correct there. However you introduce the argument of O2 levels in water with no backup to it. It is true that hemoglobine has affinity to O2, which depends on the pH in the blood, so essentially, the organism plays with the pH in blood to ensure the transport of O2 to the cells and the release of CO2 to water, when that is possible. However, the hemoglobine is not available if it is not able to get rid of the CO2, thing that cannot happen, by law of gradients, if the CO2 levels in water are high enough, which is what controls really the capability of breath of the fish. The increment of the cardiovascular activity it in intended to compensate the reduction of this gradient: Given a rate of flow of CO2 between water and gills, the only way to increment this rate is by incrementing the flow of water through the gills, as well as the blood circulation, i.e. incrementing in the cardiovascular rhythm plus more movement of the gills, which is observed, and well explained in both papers I put.

Secondly, the mechanism itself is only possible by the changes of entropy in the molecules in the process. The fishes are able to pump the oxygen inside the organism by a mix of the O2 gradient plus using a proton pump that is fed... I will let you guess... by the additional proton that is released when diffusing the CO2 in the form of HCO3- to the water, which acidifies the pH of the blood, allowing the hemoglobine to be susceptible to oxidation. If this diffussion cannot happen, then there is no way to aborb oxygen to hemoglobin due to both factors: The lack of hemoglobine available for it, plus the interruption of the proton pump through the cell membranes to allow the "forced" diffussion of O2. Fishes have this mechanism because the concentrations of O2 in water are very low respect, for example, the atmosphere, so they link both systems in a way that improves the efficiency of the system.

So sorry, your argument is not valid in global context, and only valid at specific ranges of CO2, which are not the ones we usually keep in aquariums. Our tanks saturated in CO2 will not be compensated by adding more O2. The aireation helps to reduce the CO2 concentration in water, which is most likely the side effect that really helps, more than the increment of O2 in water.

I agree, as I already did, that additional O2 helps to fishe but not for a mere physiological reason: It is due to specific receptors in the gills that triggers a hormonal response of the fish to the environmental conditions. The fishes relax (or reduce their stress) only when both CO2 levels are easily reduced in blood and O2 is available enough, i.e. only when the levels of both gases are in a specific range of values, usually, the higher the O2, the lower the CO2. This response cannot be mistaken with the physiological mechanism of  breathing, which is driven mainly by the capability of the fish to diffuse CO2 to water, i.e. linked to the concentration of CO2 in water, and not to the O2 levels in water, which only helps in given intervals of CO2 that are not the ones we usually keep in planted aquariums.


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## Bacms (24 Oct 2015)

Thank you Manuel and Clive for the clarification. I managed to get stable levels of CO2 at around 6.9 close to the substrate and constant during the photoperiod. What I did notice was that the TDS and KH oh the water was higher towards the end of the week which I first assumed was due to EI although the rising was pretty high. Well...turns out that the sand that came when I bought second hand seems to be coral and so it is buffering the pH drop. Don't know what to do about it at this point as I have tropica substrate underneath and only used the sand in the front where the HC is attached. 

I did lost three ottos tonight don't know why and can't find the body of one of them which is probably realising ammonia. I am really down today because of all this

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## zozo (24 Oct 2015)

Reading al this i come to think our fish could use some EPO and spinach...


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## Manuel Arias (24 Oct 2015)

Bacms said:


> Don't know what to do about it at this point as I have tropica substrate underneath and only used the sand in the front where the HC is attached.



Do you have lot of sand or just a small layer? Depending on that, and how deep goes in your substrate, then maybe you can suction it using a tube and "pumping" water at the same time. Its is likely the easier process to remove that sand on the top and replace it by an inert sand.



Bacms said:


> I did lost three ottos tonight don't know why



I am sorry hearing that, and hopefully the community can give you a solution. Optimal pH for Ottos is between 6 and 8. If during the night the pH is increasing for long time around 9, maybe is too agressive for those fishes... This will happen if you turn off the CO2 and you have a high kH and the CO2 is removed of the water by agitation and/or aireation. On the other hand, if you do not turn off the CO2 in the night, the problem can be that the pH goes too low for the kH values you have, saturating he water with CO2 and then suffocating the fishes. But this is just a guess from what you have mentioned here, as it might there be different causes. Note that a pH of 6.9 with a kH of 8 or higher it is enough to kill fishes for this reason. In general high kH and low pH values are a fatal combination.


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## Bacms (25 Oct 2015)

The problem with vacuum out the sand is that there is tropica substrate underneath so it can get quite messy. I have done a separation between the soil and the sand so there is about the centimetres at the front of the tank which goes all the way down to the bottom so quite a lot of it. 

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## alto (25 Oct 2015)

This discussion really isn't complete without _some_ understanding of Fish Hemoglobins 

*Braz J Med Biol Res, June 2007, Volume 40(6) 769-778  (Review)*

*Fish hemoglobins *

P.C. de Souza and   G.O. Bonilla-Rodriguez


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