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Maxing CO2 in Low Techs

Tim Harrison

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Thanks Darrel.
I ain't got no bubbles at all as I've gone back to low tech!!!
It's just that I worked with CO2 in one way or another for a number of years and suddenly thought about it laying as a blanket on the top of the water.


Oh...I sorta misunderstood before...I think:confused:...
 
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Well, if it sat there and if a little was absorbed, it's all going to help, I guess?

Where are you from OB?

On your flickr, you have pictures of bluebell wood, which looks very much like blue bell woods located in Richmond, North Yorkshire.
 

faizal

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Wow,..so many technical stuffs here.....these are new to me. So ,...the new way to go for low tech ( i.e. to increase our chances of growing a nice carpet of crypt parva or e. tenellus or saggitaria subulata) would be to make sure that we have the following?

1. A nice wide shallow tank
2. Lots of surface movements
3. wet/dry trickle filter to increase the co2 concentration within the water column. ???

This will enable us to grow carpets??? Did i get this right?

Can we run an airline with O2 during the lights out period for say 3-5 hrs to increase the chances of gaseoeus exchange with the environment or will this turn out to be counter productive as it might gas out the nocturnal accumulation of co2? It really shouldn't matter right ? ...because if we have a trickle filter,....the gasses are gonna get gassed out anyways ....right? I am so confused now:wideyed: :facepalm:
 

dw1305

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Hi all,
This will enable us to grow carpets??? Did i get this right?
I think Tom and Alastair have had success with carpets, I've never had any joy at the bottom of the tank, but my tanks are always jungles, so I don't really have any suitable spaces. Hemianthus did fine for me on top off an HMF sponge, but had access to aerial CO2.
Can we run an airline with O2 during the lights out period for say 3-5 hrs to increase the chances of gaseoeus exchange with the environment or will this turn out to be counter productive as it might gas out the nocturnal accumulation of co2? It really shouldn't matter right ? ...because if we have a trickle filter,....the gasses are gonna get gassed out anyways ....right?
That's right, we are aiming to have a large gas exchange surface to volume ratio, so that levels of all dissolved gases more closely follow the atmospheric levels at all times.There is a good page on dissolved gases here: <Aquatic Chemistry>.

This method differs from Diana Walstad's initial idea that you could have an organic rich sediment that produced CO2 (from the oxidisation of OM), and then minimal water movement retained this in the water column. I'm a great fan of hers, but I don't think this is a viable technique, mainly because you are likely to end up with problems with low oxygen levels outside of the photo-period.

I'm more than willing to trade any night-time build up of CO2 (and loss of DO.) for high(er) oxygen levels during the night.

The combination of heavily planted tanks, constant high levels of oxygenation, and regular water changes, mean that you can maintain very clean water with minimal BOD. This will lead to sub-optimal plant growth, but you can then use the "Duckweed Index" <Low maintainence, long term sustrate | UK Aquatic Plant Society> to maintain some plant growth.

There is a more complete explanation of this in: <plecoplanet: Aeration and dissolved oxygen in the aquarium> I wrote this specifically for keepers of rheophilic plecs, but it is relevant for most fish keeping.

These are KISS solutions to aquarium maintenance.

cheers Darrel
 

BigTom

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Funny this thread got bumped, I'm right in the middle of a little trial to see what effect shutting off the flow/surface movement has on the pH (as a proxy for CO2) in my tank. On the second day of monitoring pH with the usual flow setup, if it agrees roughly with yesterday's results I'll shut off the filter at lights out tonight and see if it makes a change tomorrow.

As for carpets, I've had far more luck with flow then without, although it still seems pretty hit and miss as to which species do well (Lilleaopsis is a safe bet, and Glossostigma is doing OK this time with flow).
 

roadmaster

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I run Hydro sponge filter's at night on timer in low tech heavily planted tank's.
Some argue that plant's should provide enough O2 during the day, to carry the plant's,fishes O2 requirement;s for evening but I have seen no harm from supplying a bit more O2 through exchange at surface via the sponge filter's at night ,so I continue.
Fishes/plant's thrive.
 

BigTom

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I just did an experiment, sort of. I've stated a couple of times previously purely on the basis of intuition that I reckoned a shallow tank like mine with a reasonable amount of flow would probably be fairly good at keeping CO2 levels somewhere around equilibrium.

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. Readings were taken from the exact same spot and depth in the tank (an area of open water near the center of the tank, halfway down the water column) using a Hanna 98129 meter which was calibrated once at the beginning of the experiment.

Assuming a constant alkalinity and not too much drift on the pH meter, the change in pH should predominantly reflect changes in the concentration of CO2 in the water. I realise this is a simplified interpretation, but please correct me if I've got it completely wrong.

Here are the results (photoperiod designated by orange bars) -

5cxa.jpg


Here's the same data expressed in terms of estimated CO2 levels relative to the maximum estimate observed, assuming a stable KH and everything else that might effect pH readings! (I don't have a KH test so can't give actual units):

mmno.jpg


So what does this show? Well firstly it appears that even with a shallow tank and a reasonable amount of flow and surface ripple there is still quite a strong diurnal fluctuation in pH (CO2), with the estimated CO2 level nearly halving between lights on and lights off.

Secondly switching off the flow does appear to increase the amount of CO2 available, but the plants didn't seem to use that much more of it.

Caveats: I've probably got something totally wrong; this is only a short term experiment so it's hard to say how things might change if I left the filter off; do plants take a while to adjust to increased CO2 availability?

Anyway, I'm not exactly suffering from a lack of plant growth so the filter will be going back on in the morning, but I thought people might be interested. If anything this has got me thinking about increasing surface movement as it demonstrates how hard it is to maintain stable levels of dissolved gasses and O2 is far less soluble than CO2.

And now to bed! I shall look forward to waking up to seeing Darrel and Ceg have replied and pointed out that I'm talking all kinds of gibberish :D
 

dw1305

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Hi all,
Brilliant. Looking at the cluster of points I don't think you need to run the experiment any longer. I think you are right, in that the pH changes are directly attributable to the changing oxygen/CO2 ratio.

cheers Darrel
 

Andy Thurston

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faizal

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....
So what does this show? Well firstly it appears that even with a shallow tank and a reasonable amount of flow and surface ripple there is still quite a strong diurnal fluctuation in pH (CO2), with the estimated CO2 level nearly halving between lights on and lights off.

Secondly switching off the flow does appear to increase the amount of CO2 available, but the plants didn't seem to use that much more of it.

So,...Tom,...does this mean that we :

1). should still go for a wide shallow tank

2). maintain just a mild to moderate flow in the tank like a pump rated 5-8 times the tank volume per hour (i.e. not 10 times the tank volume turn over rate)

3) make sure that the surface ripple is kept at a minimum

4) Ensure proper distribution of flow throughout the tank (i.e. spraybar along the back glass of the tank / strategically placed lily pipes etc?

5) We can still use the trickle filter to enhance the gaseous exchange ability provided by the shallow tank?

I really want to give this idea a shot y'know?. I've already ordered for a tank 36 inches long, 22 inches deep , 15.5 inches in height:) . I sort of calculated the surface area per volume ratio (S.A.P.V.R) of Alastair's puddle & these figures brings me close that .....probably off by 0.01 or so I think.
 

faizal

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Thought I'd put my spare drop checker in my low-energy tank just out of curiosity this is the result below 1hr after lights on - after a 4hr siesta period. I'd say it was "insufficient" on the colour chart...but I'm surprised it registered at all in a low-energy tank...

10595288464_dafbb8089e_c.jpg

Troi,.. could you be kind enough to show how much of a surface ripple you have there in this tank please?
 

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dw1305

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Hi all,
make sure that the surface ripple is kept at a minimum
I'm not sure, if you had a trickle filter it would be pretty efficient at out-gassing the CO2 what-ever else you do. My suspicion would be that the differences that Tom recorded are at least partly to do with the degree of oxygen saturation, rather than purely the reflecting a higher level of CO2 with the filter off. The reason I think this is that the shapes of the curves, with filter on and off, are both pretty similar. I think if you were getting a lot more dissolved CO2 with the filter off, you would have a much more "peaky" curve in that state.

I'll have a go over the weekend with a pH meter (on a standard 60cm long x 30 wide x 45 high). The tank will start with much softer water than Tom's and will be equally heavily planted.

If they aren't in use I'll borrow a lab. standard DO meter as well.

cheers Darrel
 

BigTom

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I think if you were getting a lot more dissolved CO2 with the filter off, you would have a much more "peaky" curve in that state.


That's what I was expecting to see. I must admit I hadn't really considered the role of oxygen in all this - my understanding was that it's effect on pH was relatively small compared to CO2, have I got that wrong? I had been wondering if the similarity in the graph shapes was due to the plants actually being limited by light or nutrients, rather than CO2, or perhaps that they required some time to adjust to altering levels of CO2 that are different to what they normally encounter day to day? Unfortunately my understanding of both chemistry and plant physiology falls over at this point.
 

BigTom

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So,...Tom,...does this mean that we :

1). should still go for a wide shallow tank

2). maintain just a mild to moderate flow in the tank like a pump rated 5-8 times the tank volume per hour (i.e. not 10 times the tank volume turn over rate)

3) make sure that the surface ripple is kept at a minimum

4) Ensure proper distribution of flow throughout the tank (i.e. spraybar along the back glass of the tank / strategically placed lily pipes etc?

5) We can still use the trickle filter to enhance the gaseous exchange ability provided by the shallow tank?

I really want to give this idea a shot y'know?. I've already ordered for a tank 36 inches long, 22 inches deep , 15.5 inches in height:) . I sort of calculated the surface area per volume ratio (S.A.P.V.R) of Alastair's puddle & these figures brings me close that .....probably off by 0.01 or so I think.


Faizal there's no way I would want to try and pass something off as a conclusive answer with the meager data at hand, and I'm not sure I even concluded anything from the tests other than that no flow = lower pH. I think your tank has really nice dimensions and it should be possible to produce very good results with it. With my shallow tank I've had success both with and without flow. Many plants seem to do fine with zero flow, but with trickier ones such as glosso I've definitely had more success with flow. I also think that plants are generally the easy part and worry more about my livestock, so would err towards maximising O2 via plenty of surface movement and/or a trickle filter. I like the wide steady flow that my spraybar gives so would recommend one of those also.

It may not provide maximal CO2, but it seems to be fine for these style of tanks.
 

Tim Harrison

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Troi,.. could you be kind enough to show how much of a surface ripple you have there in this tank please?

Hi Faizal, I have the spray bar near the surface slightly angled up so there is a fair ripple across the surface...although it doesn't necessarily appear so on this image. The tank is 90l and the filter is rated at 1000l/h; it's made by APS so perhaps that should be taken with a slight pinch of salt. However, you can see the tall crypts at the back bending to the flow, which should also give you some idea.

11519710826_6c86f2dda9_b.jpg
 

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faizal

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Hi all, I'm not sure, if you had a trickle filter it would be pretty efficient at out-gassing the CO2 what-ever else you do. My suspicion would be that the differences that Tom recorded are at least partly to do with the degree of oxygen saturation, rather than purely the reflecting a higher level of CO2 with the filter off.

Cheers Darrel.:) Wow,...this is really complicated isn't it. Never thought that O2 would play a significant role in a tank's pH level.
 

faizal

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I think your tank has really nice dimensions and it should be possible to produce very good results with it.

Cheers Tom:)...it is very comforting to get that approval.

........so would err towards maximising O2 via plenty of surface movement and/or a trickle filter. I like the wide steady flow that my spraybar gives so would recommend one of those also.

It may not provide maximal CO2, but it seems to be fine for these style of tanks.

Tom what's the filtration rate of your filter? Is it 10 times or more?
 

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