• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up

Maxing CO2 in Low Techs

Hi all,
I'm a little surprised that more people don't use any kind of sump system, where it's possible to "super aerate" the water using a simple skimmer (just using the venturi for aeration not actual skimming). This would definitely maximize CO2 exchange and could be used on a timer to match photo periods if so desired.
I agree. I like as large a gas exchange surface as possible and for that reason I like "wet and dry" trickle filters, although mine used to be over-tank rather than in a sump.

All the details are in this current thread, but have a look here:<Alfagrog for reducing Nitrates? | Page 2 | UK Aquatic Plant Society> for a quicker summary and picture.

I think the main thing for planted tank keepers is that we don't tend to struggle with oxygen levels the way that people with non-planted tanks do. The reasons for this are numerous, but probably the most relevant are that at the end of the photo-period the water will be fully oxygenated, and the plants will have absorbed a lot of the NH3 that otherwise would have entered microbial oxidation.

Also we differ from marine aquarists in that higher plants have a much higher net productivity than algae like Chaetomorpha, or even an "algal scrubber", fresh water holds more oxygen than salt water, and water changes are fairly trouble free and inexpensive for us.

I'm not contemplating going down the salty route, but if I ever did it would be in a system with both a trickle filter and a planted reverse lighting period refugium.

I'm always advocating "plants as the answer", but on Cichlid and Catfish keeping forums a lot of people keep fish that need good oxygenation, but for some reason are adverse to having plants for all sorts of reasons, mainly fairly spurious. That was why I wrote this <plecoplanet: Aeration and dissolved oxygen in the aquarium> (also linked in earlier in the thread).

cheers Darrel
 
Darrel,

I was one of those cichlid,catfish,pleco keeper's.(still am actually)
My effort's at keeping plant's with these fishes were thwarted in large part, by the fishes propensity for digging up substrates and my own ignorance with respect to what plant's were trying to tell me.
I am thank's to folk's here,,largely more successful with the weed's.
 
Hi all
My effort's at keeping plant's with these fishes were thwarted in large part, by the fishes propensity for digging up substrates
That is a common one,
my Pacu, Mbuna, Midas Cichlid, Plec, Koi etc. digs up/eats all my plants
and it is true, you do need to physically separate plants and fish, and that isn't always possible within the space available.

cheers Darrel
.
 
So it is established that gas exchange does good. What would be the best for a low tech no co2 and no liquid carbon tank....aeration, surface agitation or surface skimmer?

Thanks
 
I think it is established that most gas exchange takes place at the surface - so whatever is moving the surface of the water more is going to produce the most gas exchange. Therefore it will depend on which particular set-up you utilise breaks the surface tension and circulates water the most. My vote for most situations would be vigourous aeration.
 
Hi all,
What would be the best for a low tech no co2 and no liquid carbon tank....aeration, surface agitation or surface skimmer?
The best technique is probably <"laminar flow">, but I don't think it really matters which route you go down. My suspicion would be that "frothhelmet" is right and that, out of your options, vigorous aeration is the best bet.

What you want is a system that efficiently circulates water to the gas exchange surface.

If you have direct aeration, via an air pump or venturi, you want very small bubbles with a long retention time in the water column. I like a venturi, partially because you end up with a lot of air bubbles trapped under leaves, and on the filter sponge etc.

Oxygen is fairly slow to diffuse into the water, but CO2 will diffuse more rapidly from trapped air pockets, and a fine leaved plant (or an Amazon Sword etc), may benefit directly from the CO2 trapped at its leaf surface.

There is a more complete answer in:
cheers Darrel
 
Last edited:
Hi all, The best technique is probably <"laminar flow">, but I don't think it really matters which route you go down. My suspicion would be that "frothhelmet" is right and that, out of your options, vigorous aeration is the best bet.

What you want is a system that efficiently circulates water to the gas exchange surface.

If you have direct aeration, via an air pump or venturi, you want very small bubbles with a long retention time in the water column. I like a venturi, partially because you end up with a lot of air bubbles trapped under leaves, and on the filter sponge etc.

Oxygen is fairly slow to diffuse into the water, but CO2 will diffuse more rapidly from trapped air pockets, and a fine leaved plant (or an Amazon Sword etc), may benefit directly from the CO2 trapped at its leaf surface.

There is a more complete answer in: cheers Darrel

Thanks!

What is a venturi?
 
Ok I found out what it is.

Now I am confused...

What increases O2 and CO2 levels in a tank? The surface breaking? Doesn't vigorous surface agitation remove CO2 from water? Also, will O2 not increase with an airpump? I mean a venturi blows O2 into the water which presumably will increase O2 levels but will CO2 levels remain the same?
 
From my understanding... Surface agitation will increase gas transfer. So, if your water is higher in CO2 than the air, you will loose CO2 from your water. However, if your water is lower in CO2 than the air, it will increase the CO2 levels within your water.

It's the same principle for an airstone only your adding oxygen to the water rather than CO2


Sent from my iPhone using Tapatalk
 
Hi all,
From my understanding... Surface agitation will increase gas transfer. So, if your water is higher in CO2 than the air, you will loose CO2 from your water. However, if your water is lower in CO2 than the air, it will increase the CO2 levels within your water.
That's it.

The actual dynamics will be different for every tank, mainly because there are a lot of variables (tank surface to volume ratio, water turn over, efficiency of biological filtration, plant mass, fish mass, OM content of the substrate etc.), but the principle is the same.

In a planted tank, during the photo-period, plants are net oxygen producers and CO2 users (when PAR exceeds the <"light compensation point">). During this time period dissolved CO2 will be depleted by photosynthesis, and submerged aquatic plant growth will be carbon limited.

Carbon dioxide will be added to the water by respiration of the bioload and diffusion from the atmosphere at the gas exchange surface, but even in a relatively sparsely planted tank any CO2 will be quickly utilised.

If we increase the area of the gas exchange surface more CO2 will diffuse into the water.

Outside of the photo-period the reverse will happen, CO2 levels will rise and dissolved oxygen will be depleted by the bioload, but if we can get a high enough surface area to volume ratio, levels of all dissolved gases in the water will be very similar to the level of atmospheric gases.

If we aren't adding CO2 this is an advantage for plant growth during the day, and for dissolved oxygen levels at night.

This is also why "wet and dry" trickle filters are so effective for biological filtration, they have a huge gas exchange surface area.

There is a good discussion of dissolved gases in <"FAO: Aeration and oxygenation in aquaculture"> and at Wikipedia <"Water aeration">.

cheers Darrel
 
So if we encourage high oxygen levels in our non co2 tanks via surface agitation it would make sense that bacterial breakdown of rich soil sediments would be maximised. Some of the Co2 produced in this manner would/could still be utilised by plants before it has a chance to reach atmosphere? Or would we reach a point where co2 is off gassing faster than it is being produced. Surely the plants would still get some of the co2 produced via bacterial activity?
 
As you probably know CO2 level in atmosphere is more than 300 ppm so by good surface agitation you are encouraging not only O2 but CO2 as well. It is way more significant than from bacterial brakedown.

I would dispute the "way more significant" part of this statement......Do you have any scientific data to support this theory, i.e. surface agitation provides more usable co2 to plants than that from the breakdown of organics?
In practice you can blow as much surface agitation as you like and you won't achieve the same amount of healthy growth as in a planted tank with organic soil, even if you dump all your dry ferts into the tank trying to help it. There are reasons why co2 is considered so precious. It goes out as fast as it enters via surface agitation. But plants can take it via the roots in the soil where it is trapped after being produced by microbial activity. A recently planted tank with organic soil "bubbles" with co2.

The surface agitation is always about oxygen, not about co2. O2 is harder to dissolve but stays in the water longer unlike co2. If surface agitation was able to drive 1/5th of the atmospheric co2 into the water at any given time, even once in a few years, , it would kill all your fish.
 
Last edited:
I'm not really disputing the organics vs equilibrium theory just that if we aim for equilibrium levels of co2 this does not mean that plants are not getting co2 via soil breakdown at the same time.
 
"Higher concentrations of CO 2 in bottom sediments (as a result of microbial activity) are also exploited by some macrophytes (e.g., Isoetes) whereby CO2 in the interstitial sediment water diffuses into the roots and then through gas-filled lacunae to the leaves (Raven et al., 1988)"

Isoetids utilize their roots to take up carbon dioxide from sediment porewater (Wium-Andersen 1971; Søndergaard and SandJensen 1979; Raven et al. 1988), and concomitantly release oxygen from their roots, thus raising sediment redox potential (Wium-Andersen and Andersen 1972; Tessenow and Baynes 1978; Sand-Jensen et al. 1982). Relatively high redox potential (Eh) in porewater near the sediment surface can limit the release of mineral nutrients (e.g., ammonium and phosphate) and redox-sensitive metals (e.g., iron) into the water column (e.g., Mortimer 1941; Wetzel 2001). "
 
Back
Top