People with DO meters

[Habib]

Although the

reefs dimensions are small, the high density of organisms causes the oxygen concentration

of water flowing over it to vary by up to 50%. Where, Excess production over respiration

during daytime causes oxygen concentration to rise well above open-sea values. During

the night, respiration causes the depletion of oxygen to below open-sea values.


The above and real-time data (although don't get the O2 scale?) :

http://www.iui-eilat.ac.il/pp/rt-datastation.htm

[tatuvaaj]

Habib,

Thanks again!

That's kind of what I expected, shallow lagoons experience large DO changes. Some of the lagoons don't get much fresh sea water from the ocean.

It is interesting though that the atmospheric exchange plays (to me) surprisingly small part in the DO levels.

[Habib]

Tatu:

You're welcome.

IIRC Fossa and Nilsen have a graph of O2 (day night variation) in their book and I think I commented to Alf Nilsen about the absolute values a long time ago.


One which might prove to be useful:

The Biological Bulletin, Vol 179, Issue 1 148-158, Copyright © 1990 by Marine Biological Laboratory



Diffusion Limitation and Hyperoxic Enhancement of Oxygen Consumption in Zooxanthellate Sea Anemones, Zoanthids, and Corals
J. M. Shick
Department of Zoology and Center for Marine Studies, University of Maine, Orono, Maine 04469-0146

Depending on their size and morphology, anthozoan polyps and colonies may be diffusion-limited in their oxygen consumption, even under well-stirred, air-saturated conditions. This is indicated by an enhancement of oxygen consumption under steady-state hyperoxic conditions that simulate the levels of O2 produced photosynthetically by zooxanthellae in the hosts' tissues. Such hyperoxia in the tissues of zooxanthellate species negates the effect of the diffusive boundary layer, and increases the rate of oxygen consumption; thus, in many cases, the rate of respiration measured under normoxia in the dark may not be representative of the rate during the day when the zooxanthellae are photosynthesizing and when the supply of oxygen for respiration is in the tissues themselves, not from the environment. These results have implications in respirometric methodology and in calculating the rate of gross photosynthesis in energetic studies. The activity of cytochrome c oxidase is higher in aposymbiotic than in zooxanthellate specimens of the sea anemone Aiptasia pulchella, and this may indicate a compensation for the relative hypoxia in the tissues of the former, enhancing the delivery of oxygen to the mitochondria from the environment.

[Habib]

There is even the full article of the above version and at first sight looks quite interesting:

http://www.biolbull.org/cgi/reprint/179/1/148

[Boomer]

J. M. Shick

I have that article also in printed form, forgot about it I have his book also, he discussesit in there.

A Functional Biology of Sea Anemones (1991)

[beaslbob]

Originally posted by tatuvaaj
Habib,

Thanks again!

That's kind of what I expected, shallow lagoons experience large DO changes. Some of the lagoons don't get much fresh sea water from the ocean.

It is interesting though that the atmospheric exchange plays (to me) surprisingly small part in the DO levels.

No suprise here. But then my experiences are different. I have seen (admitedly FW) fish at extremely high concentrations all with normal respiration in tanks with no circulation, no other filtration, just plants.

In salt I noticed the same thing only it was the addition macros to consume the carbon dioxide. Even though the consumption was only during lights on, the daytime ph rose from 7.4 to 8.4 and has stayed there. Same circulation, same tank, the only difference was the addition of the macros. The macros consuming the carbon dioxide was more effective then circulation.

[Boomer]

addition macros to consume the carbon dioxide

And what do they give off, you forgot that part Bob, O2

[beaslbob]

Originally posted by Boomer
addition macros to consume the carbon dioxide

And what do they give off, you forgot that part Bob, O2

Yes and that was intentional. The oxygen given off by plant action IMO does not substantially increase the dissolved oxygen in the water. And a large portion of the oxygen is given off a bubbles that simply rise to the surface without dissolving in the water.

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface. Therefore, increasing the oxygen relative to the carbon dioxide. After the carbon dioxide from the animal life is consumed then the carbon dioxide from the air is consumed lowering the carbon dioxide below ambient values. And, of course, increasing the oxygen (and nitrogen for that matter) portion of the dissolved gasses in the water column.

[Boomer]

Pants, if you have enough of them, can impact the O2 quite a bit and bring O2 above sat.

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface. Therefore, increasing the oxygen relative to the carbon dioxide.

No, not really. The level of O2 or CO2 have no effect on one another. Each gas has their own partial pressure and solublity rate.

After the carbon dioxide from the animal life is consumed then the carbon dioxide from the air is consumed lowering the carbon dioxide below ambient values.

The only thing that is going to lower the CO2, is plants or if the partial pressure of CO2 in the water is high enough, then CO2 will get " blown off", which either will increase the pH. This has no effect on O2 at all.

[jfinch]

Yes and that was intentional. The oxygen given off by plant action IMO does not substantially increase the dissolved oxygen in the water. And a large portion of the oxygen is given off a bubbles that simply rise to the surface without dissolving in the water.

How can you not be sure that the water is O2 saturated (from plant photosynthsis) at that point?

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface....

The amount of CO2 in the water isn't a funtion of O2 and vice-versa. It's a funtion of temperature, salinity and partial pressure of the gas in the atmosphere.

[beaslbob]

well I never was a chemistry expert.

thanks for your information.

I was repeating articles a read several years ago and perhaps the memory is not all that clear.

Help me here:

As I understand it the total presure in the sum of the partial pressures.

What you are saying is that as carbon dioxide is produced or consumed it escapes or is sucked in to maintain the same partial pressure. So that no change is carbon dioxide partial pressure is possible given the same air at the air/gass interface.

And the same thing would apply to oxygen. As oxygen is consumed or produced it escapes or is sucked in to maintain the same partial pressure.

So it doesn't make any difference what we put in our tanks, the partial pressures keep the makeup of the dissolved gasses constant.

Further, that say we heat the water to boiling (0 dissolved gasses). Then we put that water under a 100% nitrogen atmosphere and allow it to cool to room temperature and equalize. the result would be a 100% partial presure of nitrogen. And that would also be the total pressure. For the sake of consistancy the room temperature pressure of the nitrogen is one atmosphere. This would result in the same amount of nitrogen in the water as water under air at one atmosphere.

Could be, been long time since chemistry and physics classes.

Whatever the mechanism, I know from experience that fish stopped breathing heavy and daytime ph rose and stabilized to 8.4 with the addition of plant life. And only with the addition of plant life.

Geesh now this is different from what i read before. And just to make it worse boomer tells the wife about a do meter.

[Randy Holmes-Farley]

I expect that water that has O2 bubbles in it is at or above saturation with O2. Otherwise, they would not form in the first place. All O2 coming off of algae is originally dissolved in the water, and only comes out if the water is at or above saturation. Also, if the bubbles did form somehow below saturation, they would then dissolve.

[beaslbob]

Originally posted by Randy Holmes-Farley
I expect that water that has O2 bubbles in it is at or above saturation with O2. Otherwise, they would not form in the first place. All O2 coming off of algae is originally dissolved in the water, and only comes out if the water is at or above saturation. Also, if the bubbles did form somehow below saturation, they would then dissolve.

thanks randy.

And just for the record (because I forgot to mention above) I do agree. And it does make sense.

But also is it only locally the oxygen is supersaturated? Sounds like circulation would help.

[beaslbob]

woops double post. mods please delete.

[tatuvaaj]

Just for the record, I was talking about the atmospheric exchange in nature. Well, not surprising really if the waters are calm enough at night.

BTW, the actual mechanism of gas transport from the atmosphere to water column is quite complicated (laminar boundary layers, diffusion coefficients, transfer velocities, viscosity etc. etc.) and when you insert gas injection into the picture, I just raise my hands and use reverse lighting cycle in my refugium

I'm interested in DO levels in my tank however but still haven't managed to buy the kit

[tatuvaaj]

beaslbob,

You describe exactly the same I was surprised about: the data I saw suggested that the photosynthesis "controls" DO levels from 50% to supersaturation. Inside these extremes it seems that in his tank the water movement (and also differences in O2 partial pressures between the water and air) didn't have much affect. The DO levels followed pretty closely his light levels.

I always thought (ok, hoped ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.

I think we need much more data to say anything about the DO levels in reef aquariums in general

[beaslbob]

I always thought (ok, hoped ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.

And I am glad you did. Whatever the mechanism, it comes as no suprise to me. And my ph does drop to around 7.8 at night. So obviously carbon dioxide has built up.

What is important to me is that the carbon dioxide from the fish load is totally consumed and then some during the day. Whereas before I added macros to my system, the daytime ph had lowered to 7.4 and all new fish slowy deteriorated and after a couple of weeks started breathing heavy, developed white spots then died the third week. I now think they were basically sufficating.

With plant action consuming carbon dioxide and releaseing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

[Boomer]

With plant action consuming carbon dioxide and releasing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

So it doesn't make any difference what we put in our tanks, the partial pressures keep the makeup of the dissolved gasses constant.


No, that is very incorrect Often partial pressures are not met. For example, in a FW water tank high in fish, the partial pressure will be quite high for CO2, but it will really not reach equilibrium with the atmosphere, as the CO2 can not escape fast enough. This can cause a very low pH. The O2 will not change at all. Same for a lack of CO2, were plants remove the CO2 faster than it can enter the water, from a higher CO2 pressure in the air. It is the reason behind using OC2 injection in FW planted tanks. If there is not enough CO2 in solution, as the plants are uptaking it, the plants feed off the carbonates in the water and covert it to CO2, which raises the pH. The O2 will increase but it is due to the plants giving it off.

I always thought (ok, hoped ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.

It can in many system, it depends on then load. That is, keeping it high enough form them to do Ok, as long as there is not excessive CO2 build up, followed by a low pH.

With plant action consuming carbon dioxide and releasing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

It does but it is the plants doing it. If you take a sample of water high in CO2 and then blow it off with an airstone the O2 will increase, but this not because you removed the CO2. O2 enters the water easily with aeration, CO2 or not.

Whereas before I added macros to my system, the daytime ph had lowered to 7.4 and all new fish slowly deteriorated and after a couple of weeks started breathing heavy, developed white spots then died the third week.

Yes, the pH was to low, due to pH, which caused the blood to become acidic. Normally at night the O2 levels are lower also. Under theses types of conditions, the Bohr and Root Effect also start to go astray, lower the O2 in their blood even more, which makes the CO2 uptake even more dangerous. A Triple Whammy

But also is it only locally the oxygen is supersaturated? Sounds like circulation would help.

More circulation would drive it off so as it is already 100 %, the O2 may become lower.

As I understand it the total pressure in the sum of the partial pressures

Yes, but is not that simple. O2 is easily increased in water via aeration, where as CO2 is easily drive off via aeration.

And just to make it worse boomer tells the wife about a do meter.

Well, did she listen Think of all the data you will get



Tatu, you said it on a nut shell

BTW, the actual mechanism of gas transport from the atmosphere to water column is quite complicated (laminar boundary layers, diffusion coefficients, transfer velocities, viscosity etc. etc.) and when you insert gas injection into the picture

Yes, that is very correct

[beaslbob]

So bottom line is that (whatever the mechanism) my fish did much better because of the carbon dioxide consumption and oxygen generation by the action of the plant life.

[Boomer]

Bob, did I tell you I lived in Huntsville for almost a year at RSA. I think I did but don't remember EOD stuff

[beaslbob]

Originally posted by Boomer
Bob, did I tell you I lived in Huntsville for almost a year at RSA. I think I did but don't remember EOD stuff

I know the eod from you signature.

I am at redstone now. Working for army avaition here.

[tatuvaaj]

Here's an interesting article by Göran E. Nilsson and Sara Östlund-Nilsson that suggests that my concern about low DO levels at night might be unwarranted:

"HYPOXIA ON CORAL REEFS AND HYPOXIA TOLERANCE IN CORAL REEF FISH"
Part of the proceedings available here: http://water.montana.edu/symposium/p...gs/default.htm

Of course it is still possible (even likely?) that some animals we try to keep do not have as great hypoxia tolerance as the fishes examined.

[Randy Holmes-Farley]

Thanks, Tatu.

[simonh]

I've had a search around but can't find any logs on my hard disk from my IKS aquacomputer during the time I was measuring oxygen levels. Unfortunatley, the probe is dead (again) so I am unable to measure at the moment. From observation I do remember the variation during a normal cycle been quite uninteresting. About the most interesting observation was that leaving the skimmer off in the day you could increase daytime oxygen levels.

I also have a Pinpoint Oxygen meter which is okay but it's difficult to do much as it doesn't have any automatic logging.

I'll see next weekend if I'm able to hookup the Pinpoint probe onto the IKS in some way and do some recording. I also have air-pressure module so it corrects for the air pressure. It also includes a setting for fresh/saltwater although you aren't able to enter the specific salinity so I assume it's tables are working on a fixed S=35 (or similar) when saltwater is selected.

P.S. If you are looking for Hach gear in Europe then www.DrLange.de should be able to give your country distributor. I use Camlab in the UK.