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Maxing CO2 in Low Techs

dw1305

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Hi all,
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?
They will, this is the situation you deal with when you work with the re-mediation of organically polluted water (commercial aquaculture, sewage treatment etc), here you have huge BOD, and concurrently a large production of CO2. Work on Eichornia has shown that the addition of floating macrophytes can turn a lagoon from a net CO2 producer to a net CO2 sink. (<"Floating Aquatic Macrophytes Can Substantially Offset Open Water CO2 Emissions .....".>)

The more CO2 you have in the water, and the larger the surface to volume ratio (gas exchange surface) is, the faster CO2 will equilibrate with atmospheric levels. Because oxygen is much less soluble than CO2, if you have an organic rich substrate you really need a large gas exchange surface, or you run every risk of asphyxiating your life stock at night.

Diana Walstad (in <"Ecology of the Planted Aquarium">) has figures from Barko & Smart (1983) ("The effects of organic matter additions to.....") for the production of CO2 from added sources of organic matter, but the authors found that the growth of submerged aquatic plants was reduced by this carbon addition, although this didn't effect plants that were emergent to the same degree.

You can have water supplies which are naturally carbon dioxide enriched, <"and they tend to have luxuriant plant growth">, even if they are in low nutrient situations.
Are we talking about CO2 in gas form or all kind of carbon based compounds that can be consumed by plants?
Scientists make a distinction between the CO2/HCO3- which are "Dissolved Inorganic Carbon" and other carbon compounds "Dissolved (or Total) Organic Carbon" (DOC or TOC).

High levels of TOC usually suppress aquatic plant grow, although some of this effect is likely to be to do with the lower levels of light in tinted water.

cheers Darrel
 

Soilwork

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Cheers Darrel. You see, I had a walstad tank that bombed out. My plants died, algae took over and I lost a couple of fish along the way that where showing signs of rapid breathing. In fact, i remember losing a fish every couple of weeks in this manner and wonder whether it was all due to low oxygen. I chose John innes no3 but have read that this soil is not the best of choices. What's more, it was unmineralised.

I don't really suppose my tap water has high amounts of carbon dioxide and it is termed as very soft by the water board. Sometimes I often wonder whether some of the success stories relating to no co2 tanks are almost 'accidental' in the sense that these people just have really good tap water.

Edit: also I have just installed a spray bar which is aimed slightly at the surface. Fluid dynamics have improved significantly and I have good sway on my plants. With the extra surface ripple my ph is not falling yet a can visually see an abundance of tiny co2 bubbles all over the tank. My drop checker also remains blue. Does this mean the plants are not getting the dissolved co2? It's hard to tell as I am also dosing 6ml easy carbo daily.
 
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rebel

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Sorry about two questions at the time. Of course I have no scientific proof it's just a theory. As is a theory that organic soil provides lots of CO2 available to plants. It provides carbon in organic and non organic compounds that plants find much easier to consume in low dissolved CO2 environment.
Hi Edwin you must mean its a hypothesis. In science, theory means an established idea usually having good quality evidence and usually part of an overall consensus.
 

dw1305

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Hi all,
My plants died, algae took over and I lost a couple of fish along the way that where showing signs of rapid breathing. In fact, i remember losing a fish every couple of weeks in this manner and wonder whether it was all due to low oxygen. I chose John innes no3 but have read that this soil is not the best of choices. What's more, it was unmineralised.
I like lean nutrients, and it could well have been low oxygen. The problem with JI No.3 is that you have a lot of potentially oxidisable material and a nitrogen source (again possibly as ammonia (NH3)).
termed as very soft by the water board
Very soft water could also be a problem as well, even with some water changes you could run out of HCO3- and nitrification would then lead to bio-acidification or "old tank syndrome". This used to be common when I started keeping fish and "aged water" was considered beneficial. I never changed any of the tank water, and used to go through cycles of fish death on a fairly regular basis every 6 months or so.
Sometimes I often wonder whether some of the success stories relating to no co2 tanks are almost 'accidental' in the sense that these people just have really good tap water.
I don't think the chemical composition of the water is that important, people have successful low tech tanks in very hard water ("Akwascape" or "Troi"), soft water ("BigTom" etc) you just need regular water changes and an indication of when plant nutrients are lacking. I've suggested the <"Duckweed Index">, as an indicator of when plants need feeding, mainly because the "Duckweed" isn't CO2 limited.
With the extra surface ripple my ph is not falling yet a can visually see an abundance of tiny co2 bubbles all over the tank. My drop checker also remains blue. Does this mean the plants are not getting the dissolved co2?
They are getting some additional CO2, which will be beneficial to plant growth, but not the level of CO2 that is required to change the pH of the 4dKH solution (indicated by the change of colour in the "bromothymol blue" pH indicator solution).

I'm not a CO2 user, but if I was I wouldn't be aiming for 30ppm CO2, <"10 - 15ppm CO2"> would still be a great increase over atmospheric equilibrium values.

cheers Darrel
 

Soilwork

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Thanks for the response. the tank is actually looking healthy for the first time in a long while.

With the amount bubbles in there there has to be a decent amount of dissolved co2. The good thing is that my fish are happier. When I could achieve a lime green drop checker my ph was 6 or possibly even lower. My swordtail would swim erratically with all fins extended and go in to hiding when I would go near the tank. Cardinals were also showing signs of fin erosion as well my swordtails.

Now the ph is stable I'm getting the best of both worlds. I'd like to attempt a no co2 tank again with the newly learned methods of increased surface agitation and better water distribution as well as weekly water changes or maybe even small daily ones such as yourself but the amount of time, money and stress it has caused me getting the tank to where it is now puts me off.
 

Parablennius

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Afternoon all

I hope you don’t mind me resurrecting an old thread but having read this through, I have an idea. Referring to the comments by ourmanflint using skimmers and Darrel about maximising gas exchange, see what you think of this. When I kept marine aquariums I started out using air-driven “Sander” counter flow skimmers driven by the excellent Rena 301 air pumps. These were far more efficient than many gave them credit for if set up properly and kept in tune, key being maximum “dwell” of the fine air bubbles ( limewood airstone) within the contact tube rather than rapid throughput. I used to extend the tubes to the max possible to increase the dwell time.

Now, they won’t skim in the marine sense but must surely saturate the water with whatever is pumped through them? In my aquarium the surface water is drawn off, over a weir into a space where the water is heated before being pulled through a 42sq. inch surface HFM, after which it is pumped back into the display. I’m thinking I could rig a skimmer in the heater section, before the filter, which would keep bubbles out of the display. I have no intention of ever using CO2 but wondered if you thought this might be worth a go to increase CO2 as I still have all my old equipment?

Cheers
 

zozo

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It doesn't hurt to try.. I got a low tech, with a trickle filter and about less then 2,5 times turnover. Naturaly the CO2 is very minimum. Also thougt a lot about it in how to naturaly increase it.. One day i came up with the, i thought, genius idea to use the co2 from the sump bacteria and pump this back to the tank. Bacteria seems to produce (poop) methane and Co2, so i thought this should accumulate in the sump above the trickle filter. So first tried it with an airpump. The constant noise drove me completely crazy.. Then i thought of an air diffusing venturi at the filter outlet and an airtube to the sump. It all worked, the sumps air got diffused into the water column. But with the venturi i had to significantly increase the turnover to 8 times to make it suck any air.
But the Co2 contents in it and what dissolves in the water is neglectable in both cases. I measured 0.1 pH drop in case one, i case two none, probalby the higher turnover also degases co2 faster.

All fun, but i did cut with the wild goose chase and just leave it to mother nature. You just can't realy force it without a pressurized system. :) And the very little things you can do, wont realy make your plants grow so much beter, you wont realy notice much difference. Getting it to an optimum is having patience and let the tank mature and provide it's own wallstad gass. :)
 

dw1305

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Hi all,
When I kept marine aquariums I started out using air-driven “Sander” counter flow skimmers driven by the excellent Rena 301 air pumps. These were far more efficient than many gave them credit for if set up properly and kept in tune, key being maximum “dwell” of the fine air bubbles (limewood airstone) within the contact tube rather than rapid throughput. I used to extend the tubes to the max possible to increase the dwell time.
Yes, size of the bubble, and dwell time, are the important parameter for gas exchange with direct aeration. I think that your idea would work pretty well.

You don't get any more oxygen, or CO2, than the atmospheric equilibrium values, but you replenish (or out-gas) them much more efficiently, so it is about as good as you can get for low tech.

cheers Darrel
 

Bart Hazes

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<snip> So I measured pH at regular intervals throughout the day for two days, and then to see what effect flow was having I unattached my filter completely and ran the tank without a filter for the next 2 days. <snip>

View attachment 25694

<snip>

This reply is to an old post (https://www.ukaps.org/forum/threads/maxing-co2-in-low-techs.29856/page-3#post-330177) that I liked. The two days of data points with filter on are very similar as one would expect if this is the routine operation of the tank. When the filter is switched off CO2 jumps up a lot before lights-on after one day and then makes an even bigger jump the second day. I expect the jumps would increase further until the daily curves become near-identical again. With filter on the CO2 decrease stops around 16:00 when, apparently CO2 has dropped to a point where plant take-up slows enough to match CO2 production. After 1 day without filter this is pushed back to 17:00 and for the second day without filter plant grows at a high pace until 21:00. The last day suggest CO2 is no longer depleted to a point where it curtails growth.

If CO2 take-up is dominated by water-air diffusion then no circulation should give less CO2 uptake, the fact that Tom sees it go up significantly indicates to me that CO2 uptake is dominated by generation within the tank by metabolism of fishes, plants and bacteria. But circulation should not reduce metabolic CO2 generation so what is going on? Do early morning CO2 levels without filter rise above ambient and the circulation stimulates off-gassing of the CO2? That doesn't feel right. Or does higher plant growth during the day generate more oxygen, leading to stronger metabolism during the night and thus more CO2. That would also explain why the early morning level on day 2 is higher than on day 1 because plant growth was still increasing.

Still it remains unclear to me what the driving effect of the filter's presence or absence is. Is it an effect on circulation or is the entire biological filtration component taken out of the equation. If the latter, would removing bacterial metabolism not give less CO2. Maybe not if the filter 'wastes' a lot of oxygen on converting ammonia to nitrate or other processes that don't release CO2. Then that oxygen can be use to produce CO2 by plants, fish, and bacteria that decompose the organics in the soil. Simple experiment, messy to interpret, but something interesting is going on.
 

dw1305

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Hi all,
Simple experiment, messy to interpret, but something interesting is going on
Yes it isn't conclusive, because it is just a snap-shot and because we can't measure the level of dissolved gases directly and have to use pH as a proxy of the CO2/O2 ratio.

My suspicion was that the differences you see mainly relate to the differing levels of dissolved oxygen.
Or does higher plant growth during the day generate more oxygen, leading to stronger metabolism during the night and thus more CO2.
There are just a lot of unknowns. Some of the oxygen used by plants for respiration is from oxygen "stored" in cells and lacunae during photosynthesis.

The simpler answer would be that the more strongly plants are growing the greater the net production of oxygen is. You can equate biomass production with oxygen production, because during photosynthesis one molecule of oxygen is evolved for every molecule of CO2 incorporated. At light compensation point net oxygen production is nil, but as PAR rises plants are massively oxygen producers as the "extra" CO2 is incorporated into carbohydrates.

It isn't a massively funded area of research but there are scientists working in this field. Have a look at Pedersen, et. al (2013) <"Underwater Photosynthesis of Submerged Plants – Recent Advances and Methods"> Front Plant Sci. 4: 140.

A further complication is that many aquatic plants have evolved morphological adaptations to distribute oxygen to roots and rhizomes situated in anaerobic substrates.

This is the rhizome of a lotus (Nelumbo sp.) (from the wonderful, but no longer updated, <"Wayne's World">), showing the gas conducting aerenchyma.

loroot2b.jpg


cheers Darrel
 
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Interesting read! Couple of questions, firstly, all taken into account here, when would be the best time to perform a water change, before lights come on or after? Just thinking if we have a small amount of co2 built up over night would it be best to let the lighting period have what's there and perform the change after lights out would be more beneficial and the extra oxygen caused by it be better through the night?

Secondly, when it comes to floating plants, keeping a fair amount of them is obviously a good thing for stripping out waste but would having too many floaters reduce the amount of gas exchange interface on the surface?
 
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Just remembered there was a third question :) If we are saying increased o2 then leads to more co2 through increased de-nitrification is there a place in a non co2 setup for those twinstar and similar products which appear to release hydrogen to break algae cell walls which then converts to o2 increasing o2 levels>co2 levels? Maybe that would be behind the claim that they are beneficial in planted aquariums.
 
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Came across this earlier and thought I would try and answer to keep the discussion going on a very interesting topic... strange how some questions never get answered here...

Interesting read! Couple of questions, firstly, all taken into account here, when would be the best time to perform a water change, before lights come on or after? Just thinking if we have a small amount of co2 built up over night would it be best to let the lighting period have what's there and perform the change after lights out would be more beneficial and the extra oxygen caused by it be better through the night?

Secondly, when it comes to floating plants, keeping a fair amount of them is obviously a good thing for stripping out waste but would having too many floaters reduce the amount of gas exchange interface on the surface?

Water changes add co2 and oxygen so its probably more complex that this. I always personally recommend adding glut (liquid co2) during a water change (and only then - nasty chemical overall which does more harm than good https://www.jbl.de/?lang=en&mod=blog&func=detail&id=123) due to its temporary algecide properties as the water change is a "time of change" for the tank good or bad which can allow algae to take hold. I've had good success personally using this strategy.

Floaters I guess would reduce available surface area for gas exchange, yes. Given the success demonstrated here with shallow tanks suspect flow becomes important too (assuming you are referring to a normal depth tank) to move co2 and/or oxygen rich water from the surface to the depths and present more opportunity for gaseous exchange by moving less co2 and oxygen rich water from the depths back up again.


Just remembered there was a third question :) If we are saying increased o2 then leads to more co2 through increased de-nitrification is there a place in a non co2 setup for those twinstar and similar products which appear to release hydrogen to break algae cell walls which then converts to o2 increasing o2 levels>co2 levels? Maybe that would be behind the claim that they are beneficial in planted aquariums.

Maybe in low tech systems but in high tech I don't believe they would help raise co2 levels beyond their already elevated position.. the debate will rage on with these units I think!... I also suspect that this increased denitrification by filter bacteria thing depends on plant mass and fertilisation and stocking levels... take an extreme example of a non fertilised planted aquarium... There isn't likely going to be enough spare ammonia knocking around for this to have much of an effect as the filter is already dealing with it all.
 
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JMorgan

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Having just read through this thread, well skimmed through to be honest, I kept noticing the oft repeated statements about dwell time and size of bubbles, small being better etc.
That reminded me of something I saw recently, which is probably very well-known to many here, but which intrigued me, not least because I do love to find an excuse for a little DIY project.

I think its safe to assume that the amount of lift generated must correspond pretty directly to the size of the bubbles and how 'saturated' the water is within the uplift pipe with air?
Obviously the intent in the video and with normal usage is to make the uplift as efficient as possible, so dwell time is very small, especially since he has this pouring over the top of an HMF.

I wonder what might happen if, instead of using a vertical pipe, you applied the same idea to a rising spiral tube, thereby considerably increasing dwell time? I think you'd want the outlet to be beneath the surface to avoid it immediately gassing off, and you could even add another venturi to the outlet, as well as disperse the flow force with a spray bar.
With a trickle filter, we're maximising water surface in contact with air, but with tiny bubbles we're maximising air surface in contact with water. I also wonder, without having even the beginnings of the maths and physics to figure it out, how depth and pressure play into this equation?

I have a 60cm cube tank standing empty and a hankering to play with a some B.smaragdina bred by a local chap. I was already thinking of using an HMF with this to give it a nice black back drop and hide the heater, but with this tank I'll want very gentle flow. So it might be a good candidate for sending the return water on a fairly long journey to combine maximising the gas exchange (for the CO2 for the plants - B.smaragdina couldn't care less about the O2) with reducing the strength of flow, whilst still keeping everything moving gently.
 

Edvet

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thinking of using an HMF
I love HMF, i run mine on cheap smal filters, either two small ones or a larger one. I use the outflow"pipe" just below the surface angled slightly upward to get some surface movement or just above to break the surface.
These:
s-l300.jpg

Very reliable and no sound.
 

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