# Overnight CO2



## Lemsip (25 Nov 2011)

Recently setup pressurised CO2 using welding canisters - I have no solenoid and I'm wondering if it will be alright to leave the CO2 on constantly (overnight when no lights are on). The cost of the gas by doing this is very small (its a 23L Fluval Edge), my concern is the fish/shrimp in the tank will suffocate.

Do you think I need an airstone?


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## Orlando (25 Nov 2011)

Its no problem, you can either dose co2 slowly 24/7, or you can also have an air pump come on at night for night time aeration for fish and plants.


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## Radik (25 Nov 2011)

No need for air pump at all. I am running 24/7 on shrimp tank and they are more sensitive than fish and are OK.


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## Lemsip (11 Mar 2012)

Resurrecting this as I've noticed my otos have a very fast breathing rate, wondered if this could be co2 related. The surface agitation in this tank is pretty poor - would adding an air pump only at night make any difference (through the day aswell?) or do you think co2 will be affected too much?


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## GHNelson (12 Mar 2012)

Hi
If you cant apply more surface agitation.
I would run a air pump during the lights out period for 3 to 4 hours using a timer and monitor the fishes breathing when lights come on.
Use a Co2 drop checker...observe what colour it is.
You need to slow your bubble rate down over the 24/7 period.
hoggie


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## foxfish (12 Mar 2012)

I would save up & buy a solenoid valve as this will not only be safer but, double the life of your gas cylinder contents.


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## GHNelson (12 Mar 2012)

foxfish said:
			
		

> I would save up & buy a solenoid valve as this will not only be safer but, double the life of your gas cylinder contents.


Yea, that would be good advice... look on this topic for information on a cheap solenoid valve.
viewtopic.php?f=23&t=20450
hoggie


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## Antipofish (12 Mar 2012)

foxfish said:
			
		

> I would save up & buy a solenoid valve as this will not only be safer but, double the life of your gas cylinder contents.



They're only about £20


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## dw1305 (12 Mar 2012)

Hi all,


> Resurrecting this as I've noticed my otos have a very fast breathing rate, wondered if this could be co2 related.


 Yes it is, _Otocinclus_ have a high oxygen requirement, and the CO2 is effecting blood oxygen levels via the *Bohr effect* "_.... an increase in blood CO2 concentration will result in haemoglobin releasing oxygen_".  The fish are breathing more rapidly to increase the volume of water flowing across the diffusion surface (the gills). The rate that CO2 diffuses out of the gill, and O2 into the gill, will depend upon the diffusion gradient from the blood to the tank water. This sub-lethal stress will weaken the fish, even if they don't directly suffocate. (Technical details in the quote from <http://www.holar.is/~aquafarmer/node1.html>, and can be skipped by those who aren't interested in fish physiology).



> _The blood flows in the ventral aorta, from the heart into the gills. The blood vessels to the gill arches and are distributed into the primary and from there into the fine capillaries in the secondary lamellae. The blood flow is in opposite direction to the water flow through the gills, so oxygen deficient blood meets oxygen rich water, which again ensures diffusion of oxygen into the blood stream. The fish can in this way extract 80-90% of the available oxygen from the water that flows through the gills. The oxygenated blood then flows from the gills into the dorsal aorta.
> 
> *Respiratory movements*
> When "inhaling" the fish opens its mouth increasing the volume of the mouth cavity, creating a suction effect into its mouth. The gill cavity also expands and finally due to the pressure difference, water flows from the mouth out through the gills. The gill cover (operculum) closes the gill cavity in such a way that the water is prevented from flowing in the wrong direction. When "exhaling" the volume of the mouth cavity is decreased, increasing the pressure, opening the gill cover and water flows out. The flow through is important as there is a constant renewal of oxygen-rich water flowing through the gills. The oxygen content of water is too little to ensure a sufficient oxygen uptake if the flow direction was in and back out through the same opening as in the lungs of land vertebrates.
> ...


Have a look here for some more details for _Otocinclus_: <http://www.ukaps.org/forum/viewtopic.php?f=35&t=12821&p=172715&hilit=darrel+otocinclus+CO2#p172715>.

Having sufficient oxygen is the fundamental requirement of fish keeping, and because of this whole thread it might be worth having a look at:
 "_*Aeration and Oxygenation in Aquaculture*_": <http://www.fao.org/docrep/X5744E/x5744e0m.htm>
 & "_*Aeration and dissolved oxygen in the aquarium*_":  <http://plecoplanet.com/?page_id=829>
Personally I don't use CO2, and this is mainly because of the risk involved for the fish if CO2 levels inadvertently rise.



> The surface agitation in this tank is pretty poor - would adding an air pump only at night make any difference (through the day aswell?)


 Yes, you need an air pump at night. During the day the water will be fully oxygenated (& CO2 depleted, if you don't add CO2) because the plants are actively photosynthesising and light levels are above LCP ("light compensation point", where oxygen production exceeds oxygen consumption). 

Radik can get away with adding CO2 at night, because his tank has a low BOD and/or very efficient gas exchange. The advantage of having the CO2 on continually, is that CO2 levels won't limit photosynthesis when the lights come on.  People with a solenoid valve will turn their CO2 on before the lights come on, again so that CO2 levels will rise and not limit photosynthesis at "lights on".

During photosynthesis plants are net oxygen (O2) producers, but at night when they are still respiring,  but not photosynthesising ("_light levels are below LCP_"), they are net oxygen consumers and contribute to the bio-load. 

*Photosynthesis*





*Respiration*




cheers Darrel


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## sWozzAres (12 Mar 2012)

Air stones create alot of surface movement, aiding CO2 to escape. If you use a venturi o2 diffuser, in theory this should reduce surface movement but wouldn't the CO2 escape into the air bubble while it's circulating the tank?


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## sWozzAres (12 Mar 2012)

oh and what's the most accurate way to measure O2?


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## dw1305 (12 Mar 2012)

Hi all,


> Air stones create alot of surface movement, aiding CO2 to escape. If you use a venturi o2 diffuser, in theory this should reduce surface movement but wouldn't the CO2 escape into the air bubble while it's circulating the tank?


Direct aeration has relatively little effect on the oxygen content of the water, air is only 20% O2, and oxygen isn't very soluble. For direct aeration to have much effect you need a very small bubble and very low residence time in the water column. CO2 is much more soluble in water (this is why you can use bubble ladders etc), but only comprises 0.03% of the atmosphere.

Solubility charts courtesy of engineeringtoolbox.com (from Clive's post here: <http://www.ukaps.org/forum/viewtopic.php?f=37&t=15903&start=10>)







Both of these devices (air stone and venturi) work by turning the water over, bringing de-oxygenated water to the surface and creating a larger gas exchange area. This is why "wet and dry" trickle filters are so effective, they have a huge gas exchange surface and will very effectively out-gas CO2.



> oh and what's the most accurate way to measure O2?


 With a dissolved oxygen meter, but they are expensive bits of kit, so realistically we can't measure oxygen content. There are certain things you can do to help maintain oxygenation.


> A high water flow rate increases gas exchange - CO2 out, oxygen (O2) in.
> 
> Biological filtration capacity is often limited by lack of oxygen, not lack of filter material, bigger is only better if sufficient oxygen is reaching all the of the aerobic bacteria in the filter.
> 
> ...


cheers Darrel


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## foxfish (12 Mar 2012)

Antipofish said:
			
		

> foxfish said:
> 
> 
> 
> ...


Very interesting!
Do you mean to refill your bottle has cost you £20? 
Perhaps you are referring to a fire extinguisher refill? or perhaps a 5gk bottle or even just a 500g bottle?
Do you count the travel & possible inconvenience of finding someone who will do the refill with the   ?
Perhaps you are suggesting it is a good idea to leave the Co2 on 24 - 7 & as the gas (in your case) is so cheap, if £20 is cheap?
Or Perhaps you mean a new solenoid only cost £20?
I actually paid over £60 for my solenoid but it is a reliable & good quality product.
Beware when purchasing Co2 equipment  as it is easy to make the wrong purchase & end up regretting you did not hold out for the better quality unit!


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## Lemsip (12 Mar 2012)

Thanks very much for the detailed response dw1305 - I will pick up an air pump ASAP. Will I need to switch off the co2 at night for the air pump to be effective? (Can it compete?) Using the cheap welding gas build so no solenoid.

I have a dropchecker in and it's always below 30ppm, I think the main issue with this particular tank is the surface agitation (Fluval Edge) so running co2 with it just makes that worse.


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## dw1305 (12 Mar 2012)

Hi all,


> Will I need to switch off the co2 at night for the air pump to be effective?


 No, it should be all right with the CO2 left on, if you turn it of you will have to re-set the bubble rate every morning.  The more surface agitation you have the more CO2 you will use, but it should ensure your fish don't asphyxiate. 

Although I'm a CO2 agnostic and don't expect ever to go high-tec, I'd agree with Foxfish about the kit, if you are serious about using CO2 it would be worth looking through the FE sticky <hhttp://www.ukaps.org/forum/viewtopic.php?f=34&t=266> and buying all the bits recommended.

cheers Darrel


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## Lemsip (13 Mar 2012)

dw1305 said:
			
		

> Hi all,
> 
> 
> > Will I need to switch off the co2 at night for the air pump to be effective?
> ...



Thanks very much - I'll grab an airpump and see how things go. Agreed I'll definitely use FE for my next build, thought I'd go with the disposable welding ones for this first nano tank.


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