More questions about oxygen

[Masha]

A while ago I got some great answers about oxygen in the aquarium

(this thread
http://www.aquariumadvice.com/forums/f12/questions-about-oxygen-279914.html)

I wanted to confirm something.

How important is surface agitation to increasing the amount of oxygen absorbed by the water? For example, in my quarantine tank I've got a pretty strong internal filter that makes the water circulate fairly strongly, but the surface is not noticeably agitated.

I'm heating that at the moment to treat a case of itch. Fish seem fine, nobody's gasping at the surface, but I wonder if it would be better to add an airstone to get more surface agitation going on?

Is it all just about circulating the water to the surface so gas-exchange can happen, or does the agitation itself help?

 

[glenCOCO]

It's the agitation that'll help with gas exchange. You can have 10000x turnover rate below the surface but if the surface is calm then there's no exchange happening, or at least not a significant amount. Some fish tolerate high temp better than others. What temp are you at? Whatever the case, you should probably just lower your water a bit so the filter can agitate the surface. It'll only make the recovery that much easier for your sick fish.

 

[Masha]

It's the agitation that'll help with gas exchange. You can have 10000x turnover rate below the surface but if the surface is calm then there's no exchange happening, or at least not a significant amount. Some fish tolerate high temp better than others. What temp are you at? Whatever the case, you should probably just lower your water a bit so the filter can agitate the surface. It'll only make the recovery that much easier for your sick fish.

I'm at 31.5 Celcius at the moment - that's as high as the heater goes. It's been there for three days now and all signs of itch are gone, and the fish all seem really good. Bright as buttons, in fact.

I can't lower the water as the filter is not a HOB - it's an internal filter. I tried lifting it's nozzle above the surface but then it just buzzes, with no water coming out

I've got an airstone in there but I don't have it on all the time, the crappy pump I've got is so loud. I really need to get a better quality pump.

 

[glenCOCO]

Wow, pretty high lol

When treating with heat only you want to keep the temp up for 10-14 days. Just keep a close eye on your fish as the days go by.

 

[flitabout]

I would get that airstone going. The higher that the temp is the less oxygen that it contains. Also try bringing the temp down to about 30c it will take care of the ich and be a bit easier to maintain the oxygen levels.

 

[Masha]

I'll do that now. Airstone is already in -- just writing about it made me paranoid!
Adjusting the temp on this heater is a pain but I'll have a go to try and get it down to 30. Will be a relief, really. I read that 3 days at 32 will kill the parasite so since the fish were looking fine I thought I'd give it a try.

 

[flitabout]

I will but you still have to keep that temp up for around 10 days to make sure that you catch every bit of it in the life stage where it is able to be killed. This is my favorite article on it. Understanding and Treating Ich or White Spot

 

[Masha]

Don't worry, I realize that
It's almost down to 30 now, going to keep it there for a week now

Thanks for the link

 

[pip walters]

The flow in the tank from the filter causes a circular flow in the tank that will 'pull' oxygen down from where it enters at the surface. However, agitating the surface will, as others have said, allow more oxygen to get in and, also important, carbon dioxide and other gasses to get out.

If a tank is covered, carbon dioxide could accumulate above the water surface. As it is more sense than oxyen, it can sit on the surface, preventing oxygen getting into the water. This higher density can also cause oxygen to be 'forced out' of suspension.

Not only that, but high levels of dissolved gases, especially Carbon dioxide can mean the fishes blood can become saturated, causing 'gas bubble' disease.

So, water surface agitation isn't just about oxygenation. you did the right thing adding the airstone

 

[Masha]

I was wondering about the hood, and moved it half off last night. Just in case!

 

[aqua_chem]

If a tank is covered, carbon dioxide could accumulate above the water surface. As it is more sense than oxyen, it can sit on the surface, preventing oxygen getting into the water. This higher density can also cause oxygen to be 'forced out' of suspension.

Not only that, but high levels of dissolved gases, especially Carbon dioxide can mean the fishes blood can become saturated, causing 'gas bubble' disease.

So, water surface agitation isn't just about oxygenation. you did the right thing adding the airstone

I'm sorry, but where are you getting this?

CO2 won't sit on the surface as you describe it. Gas is in constant motion and won't sit around like you describe. If it did, than there would be a layer of CO2 100+ feet thick sitting on the earth, suffocating us all. Instead, it constantly mixes. In the planted tank side of the hobby, we actively inject CO2 into tanks without this being a problem per se, although sometimes people get overzealous and gas their fish.

Likewise, CO2 levels never reach levels near saturation in aquaria. That would have at around 1700 ppm. CO2 levels are around 5 ppm for us, with CO2 injected tanks topping out at 70 ppm. Your describing something like the bends, which happens when inhaling pressurized gas in a pressurized environment before quickly depressurizing causes nitrogen bubbles to form in tissue.

You can run into issues in still tanks, especially if unplanted/overstocked, but that's not particularly common. It could probably happen in a hot tank without a filter, but if you've got so much as a HOB you should be covered.

I'm all for giving sound advice, but lets not do it with bad science.



To address the question at hand, water is basically playing a game a red rover on the surface, making a barrier for gases to cross. This is called surface tension. If you break up the surface tension, then you weaken the barrier and gases can cross more easily. If you don't have agitation, then some gases will get through, but at a much slower rate. In a warmer tank, gases are less soluble, so you have less of a reserve in the tank and less gas enters the tank. If oxygen levels weren't a problem before, they may still not be a problem, but if they were borderline before, they may be a problem now. Keep an eye on your fish and watch for them acting lethargic, acting funny/dopey, or breathing right below the surface of the water.



Also, the lid's not going to make a difference. People do fine with glass covers over tanks with just a tiny hole in the corner for cables.

 

[Masha]

To address the question at hand, water is basically playing a game a red rover on the surface, making a barrier for gases to cross. This is called surface tension. If you break up the surface tension, then you weaken the barrier and gases can cross more easily. If you don't have agitation, then some gases will get through, but at a much slower rate. In a warmer tank, gases are less soluble, so you have less of a reserve in the tank and less gas enters the tank. If oxygen levels weren't a problem before, they may still not be a problem, but if they were borderline before, they may be a problem now. Keep an eye on your fish and watch for them acting lethargic, acting funny/dopey, or breathing right below the surface of the water.


Also, the lid's not going to make a difference. People do fine with glass covers over tanks with just a tiny hole in the corner for cables.

Thanks, that makes a lot of sense. I was wondering about the surface tension and what difference that makes.

I'm still so inexperienced that it's difficult for me to tell when my fish are behaving unnaturally. Last night the corys were swimming around a lot, and sometimes near the surface, but this morning they're rooting around in the gravel as normal.

Must say I can't wait for the 10 day period to be over.

 

[pip walters]

I'm sorry, but where are you getting this?

CO2 won't sit on the surface as you describe it. Gas is in constant motion and won't sit around like you describe. If it did, than there would be a layer of CO2 100+ feet thick sitting on the earth, suffocating us all. Instead, it constantly mixes. In the planted tank side of the hobby, we actively inject CO2 into tanks without this being a problem per se, although sometimes people get overzealous and gas their fish.

Likewise, CO2 levels never reach levels near saturation in aquaria. That would have at around 1700 ppm. CO2 levels are around 5 ppm for us, with CO2 injected tanks topping out at 70 ppm. Your describing something like the bends, which happens when inhaling pressurized gas in a pressurized environment before quickly depressurizing causes nitrogen bubbles to form in tissue.

You can run into issues in still tanks, especially if unplanted/overstocked, but that's not particularly common. It could probably happen in a hot tank without a filter, but if you've got so much as a HOB you should be covered.

I'm all for giving sound advice, but lets not do it with bad science.



To address the question at hand, water is basically playing a game a red rover on the surface, making a barrier for gases to cross. This is called surface tension. If you break up the surface tension, then you weaken the barrier and gases can cross more easily. If you don't have agitation, then some gases will get through, but at a much slower rate. In a warmer tank, gases are less soluble, so you have less of a reserve in the tank and less gas enters the tank. If oxygen levels weren't a problem before, they may still not be a problem, but if they were borderline before, they may be a problem now. Keep an eye on your fish and watch for them acting lethargic, acting funny/dopey, or breathing right below the surface of the water.



Also, the lid's not going to make a difference. People do fine with glass covers over tanks with just a tiny hole in the corner for cables.

I am getting it from first hand experience.

I grant you, it is unlikely in aquarium as we have constant movement, but is is certainly possible when fish in bags are sitting in too much heat at an airport, for instance.

Are you saying that CO2 isn't denser than oxygen and in high levels cannot prevent oxygen dissolving?

The rest I am getting from my lecturers at university and my experience with gas bubble disease, which can even occur in nature (although rare) when instances of high pressure occur very quickly. In large fish farming warm water re-circulating systems, a layer of CO2 can actually build up in the building housing the system... it is a health and safety consideration in my line of work.

A layer of CO2 does sit up there in the sky. It may not be suffocating us, but it does cause probelms.

Oh and gas bubble disease is very much like the bends. It occurs when gases in supersaturated water escape into the body fluids of the fish and cannot escape, so are forced out of solution as bubbles in veins and arteries, as is the case during decompression in divers. With fish, it is osmotic pressure that causes the problem.

I said these things 'could' happen. You say they can't then go on to say they could in certain conditions, which are unlikely. Could they or couldn't they?

Is this bad science, or just science you haven't experienced yet?

 

[mrvincent]

The more temperature is high, the more surface agitation you require, as water lose air absorbtion capacity with temp.

In a normal temp (e.g. 21-25C° for tetra neons), a very little surface agitation is required. In my case I have 0 surface agitation and i'm dosing CO2 and I don't have surface gasping fish problems... (But my plants make lot of O2 bubbles -.-)


Gaz bubble problems can only happen if your tank is more than 6-7 ft. depth...

 

[aqua_chem]

I grant you, it is unlikely in aquarium as we have constant movement, but is is certainly possible when fish in bags are sitting in too much heat at an airport, for instance.

It might happen with fish in a bag, but only because they're in an airtight container. Then again, fish have been shipped in bags in all months and in all conditions for years, so I still wouldn't worry about it too bad.

Are you saying that CO2 isn't denser than oxygen and in high levels cannot prevent oxygen dissolving?

You're confusing things. Liquids will separate out freely if their density is different enough, but gases usually will not, at least not as discreetly as you're describing. The mechanics are different. They have higher concentrations of one level of a container compared to another, but they don't form 'layers' like you're describing.

The rest I am getting from my lecturers at university and my experience with gas bubble disease, which can even occur in nature (although rare) when instances of high pressure occur very quickly.

Changes in pressure or changes in temp can cause this to happen, but very rarely, usually in extreme conditions. But notably, this happens with gases like nitrogen or oxygen that have low solubility, never with CO2. CO2 has high water solubility, so you would have to have levels several orders of magnitude higher to cause this (100x or so). It simply doesn't happen like you're describing.

In large fish farming warm water re-circulating systems, a layer of CO2 can actually build up in the building housing the system... it is a health and safety consideration in my line of work.

A layer of CO2 does sit up there in the sky. It may not be suffocating us, but it does cause probelms.

At sea level, CO2 takes up ~.03% of the atmosphere. Hardly a discrete layer that would block O2 equilibrium like you've described. I would be interested in reading an article about CO2 accumulation in aquaculture if you happen to know of one.

Oh and gas bubble disease is very much like the bends. It occurs when gases in supersaturated water escape into the body fluids of the fish and cannot escape, so are forced out of solution as bubbles in veins and arteries, as is the case during decompression in divers. With fish, it is osmotic pressure that causes the problem.

I said these things 'could' happen. You say they can't then go on to say they could in certain conditions, which are unlikely. Could they or couldn't they?

Is this bad science, or just science you haven't experienced yet?

An osmotic shift of a magnitude enough to alter the solubility of a gas to such a degree would cause massive tissue damage before the gas bubbles were ever a problem.

Your entire argument is based on a misunderstanding of gas kinetics and CO2 solubility. Nothing you've described can reasonably happen in aquaria and isn't worth mentioning in the context of the original question, as it just adds confusion.