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Maxing CO2 in Low Techs

Hi all,
Good old air pollution...increasing the concentration of atmospheric CO2
Up from about 300ppm pre-industrial revolution, and often higher in than 400 ppm in well insulated houses.
So taking that in to account along with a realistic carbon affinity for a hypothetically typical macrophyte, etc do you reckon it'd be possible to arrive at a rough formula for calculating trickle filter size?
Probably not a formula, quite small trickle filters have the potential to deal with a lot of BOD, but in that case it is slightly different from CO2, as the wet surfaces in the filter contain the nitrifying bacteria and are using atmospheric oxygen. The CO2 they produce is out-gassed straight to the atmosphere.
Aside from that am I right in thinking water in equilibrium with air contains 0.5 mg/l CO2? If this is so, is it entirely possible - in soil substrate tanks at least with higher concs of CO2 due to decomposition - that trickle filters and tanks with large surface area:volume ratios are actually degassing CO2 to achieve equilibrium?
Quite likely, and it doesn't have to be a soil substrate tank for this to happen, any tank with a high plant load is going to have CO2 levels build up at night, unless we take measures to out-gas it. This is actually another advantage as it stops your fish asphyxiating at night. The details for the dissolution of CO2 ar here: <http://www.pwtag.org/researchdocs/Used%20Ref%20docs/52%20Carbondioxide%20in%20water%20equilibrium.pdf>.
She also said that the CO2 amount produced is higher than the one via surface movement diffusion and that's what many folks don't understand. However she first advised to eliminate surface movement in order to prevent diffusion of CO2 in air, but she recently advised she's changed her mind, and advised for surface movement and means of oxygenation explaining that it's the oxygen those tanks are having problem with. It's way less solubale in water than CO2 but it's essential for decomposition of organics, so low oxygen, low CO2 at the end of the day. Without enough oxygen, there's not enough CO2 production, plants suffer, the substrate goes anaerobic, that leads to even less oxygen, bad bacteria flourishes, fish die
I think this is a pretty good summary of where we are. I also think you need to factor dKH into this as well, Diana Walstad is using a carbonate rich substrate because nitrification uses both O2 and carbonates.
Oxygen is the key and I agree with Darrel on that as he pointed it out many times.
Yes that is really it, I'm not really interested in the levels of CO2 in my tanks, and I know that they will change dramatically during the photo-period, all I have to do is keep the oxygen levels high, have some nutrients (including CO2) and everything is OK.

cheers Darrel
 
Hi, I've been reading this with great interest, and find what Darrel is saying makes a lot of sense to my mind. I do have one very simple question, however; can you give me examples of carbonate rich substrates? No great theoretical questions, I just don't know what these substrates are!
All the best from Bill. :D
 
Hi, I've been reading this with great interest, and find what Darrel is saying makes a lot of sense to my mind. I do have one very simple question, however; can you give me examples of carbonate rich substrates? No great theoretical questions, I just don't know what these substrates are!
All the best from Bill. :D


I've never actually read Walstad, but I think in this case it just refers to the fact that the commercial soil mixes favoured in this sort of approach tend to contain limestone, which is a ready source of calcium carbonate.
 
Hi all,
I've never actually read Walstad
Go on buy a copy, every-one should own one, only £9.59 for the Kindle version. It is a bit like reading Richard Dawkins you might not agree 100% with all of findings, but 99.9% of them are pure gold dust and it is a fantastic book <Amazon.co.uk: Diana Walstad: Books, Biogs, Audiobooks, Discussions>.
can you give me examples of carbonate rich substrates?
but I think in this case it just refers to the fact that the commercial soil mixes favoured in this sort of approach tend to contain limestone, which is a ready source of calcium carbonate.
Pretty much, in her book she says
"for softwater tanks then I would advise hobbiests to use a soil that contains a source of hard water nutrients. Acidic garden soils can be fertilized with powdered dolomite lime.......for fertilizing potting soils I would use a less reactive lime source such as pelleted dolomitic lime, oyster grit or crushed sea shell"
In much of the S. and E. of the UK the soil will naturally be carbonate rich, although most of our limestones haven't undergone dolomitization (where some of the calcium carbonate is replaced by magnesium carbonate).
She likes hard water tanks because they maintain a more stable pH (personally I'm not too bothered about pH fluctuation, but she doesn't change much water, so acidification over time is more of a problem), they provide calcium, magnesium etc. and also keep any heavy metals as insoluble carbonates or hydroxides.

The book also has some figures for the extent and duration of carbon release (as CO2) from soils (on page 83).

cheers Darrel
 
It's a good reference and quite accessible without too much prior knowledge...I read it in one sitting but not sure how much actually went in though.

I need to read the rest of this. I put it down after reading a third of it and suffering with information overload.
Does anybody know if there are any differences between the 1st, 2nd and 3rd editions

I think the 2nd ed has a few colour plates at the beginning. Not sure about the 3rd ed.
 
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
 
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
Have you got a ph meter Troi? I would be interested to see a record of hourly ph changes
 
Hi all,
Have you got a ph meter Troi? I would be interested to see a record of hourly ph changes
I've never done it systematically, but in my rain-water tanks with light stocking, a reasonable amount of filtration and very heavy planting, the pH varies from about pH6.5 just before lights on to about pH8 in the middle of the light period. I don't know what the dKH is, but they are about 60 - 70ppm TDS. I assume this pH change relates entirely to the varying proportions of CO2 and O2.

cheers Darrel
 
My low-energy tank pH doesn't change much. The tap water round these 'ere parts it's rock 'ard...possibly the hardest water in the UK so it's buffered to kingdom come - but that's the south east for you. It ranges from 7.4-7.6. Obviously the water in the checker is 4dKH solution.

Come to think of it it doesn't change that much in my high-energy tank either...well not like Darrel's low-energy tanks anyway...about 7.2-6.4, and that's with pH lowering substrate as well.
 
Hi all,
Come to think of it it doesn't change that much in my high-energy tank either...well not like Darrel's low-energy tanks anyway...about 7.2-6.4, and that's with pH lowering substrate as well
That is the answer, it is just the carbonate buffering. The more dKH (H+ ion acceptors) you have the more stable the pH will be, unless you add a huge amount of acids (H+ ion donors). In the case of adding CO2, only a small amount of the CO2 will become carbonic acid (H2C03) and you need to add a lot of CO2 to drive the CO2~ HCO3 equilibrium in favour of H2CO3 and reduce the pH.

This is one of the problems with discussing pH with other fish keepers, if they keep marine fish, or Lake Tanganyika cichlids, they are dealing with systems where pH is virtually immobile, and it needs a huge change in water chemistry to change the pH. In very soft low TDS water the opposite is true, and even the additions of small amounts of weak acids (H2CO3) and bases (O2) will dramatically alter the pH.

This is partially why the whole mythology of "pH crashes" have built up and it is so difficult to persuade people that pH reduction and fish death are both symptoms of underlying bio-acidification <Bio-acidification | The Skeptical Aquarist> and acidosis, rather than the former having caused the latter.

cheers Darrel
 
Trouble with the Walstad book is that even Diana now uses circulation pumps or powerhead etc in her tanks.

I run all my non CO2 tanks these days with a 10% weekly water change. Each with circa 1.2WPG LED. No major algae problems. The odd little bit of BBA or dusting on rocks but thats it.

Similarly on a previous scape of mine I got bored with it after 6 months (was a hitec, CO2, setup) I lowered the light amount, turned off CO2, stopped regular dosing and it didn't get a water change for 14 months. Fish waste and food was the main source of nutrient and I just added a pinch of KN03 and KH2PO4 if I noticed GSA developing. That was probably every 2 months or so. Filter turnover was only 5.6x and I always like to have a ripple on the surface.

This was the last photo as a hi tec in August 2009. Mark Evans took this photograph so it maybe looks a bit better :)
full_tank1.jpg


And 13 months later (haven't got a 14month photo. lol) with no water changes since August 2009. Here is the same tank in September 2010 slightly overrun with cherry shrimp and MTS but still healthy:
DSCF1585.jpg


Further on in February 2011. Same tank still alive.
DSCF2001.jpg


All in all it had full CO2 hi tec treatment for the first 5 months and then for a one month period after the 14 months of water change then back to non CO2.
 
Trouble with the Walstad book is that even Diana now uses circulation pumps or powerhead etc in her tanks.

I run all my non CO2 tanks these days with a 10% weekly water change. Each with circa 1.2WPG LED. No major algae problems. The odd little bit of BBA or dusting on rocks but thats it.

Similarly on a previous scape of mine I got bored with it after 6 months (was a hitec, CO2, setup) I lowered the light amount, turned off CO2, stopped regular dosing and it didn't get a water change for 14 months. Fish waste and food was the main source of nutrient and I just added a pinch of KN03 and KH2PO4 if I noticed GSA developing. That was probably every 2 months or so. Filter turnover was only 5.6x and I always like to have a ripple on the surface.

This was the last photo as a hi tec in August 2009. Mark Evans took this photograph so it maybe looks a bit better :)
full_tank1.jpg


And 13 months later (haven't got a 14month photo. lol) with no water changes since August 2009. Here is the same tank in September 2010 slightly overrun with cherry shrimp and MTS but still healthy:
DSCF1585.jpg


Further on in February 2011. Same tank still alive.
DSCF2001.jpg


All in all it had full CO2 hi tec treatment for the first 5 months and then for a one month period after the 14 months of water change then back to non CO2.


How did you find that poppy inlet? Just out of interest.
 
Ok then this is the colour of the drop checker first thing before lights on...it's pretty much approaching "normal" CO2 levels, which by anyone's standards it pretty darn good for a low-energy, soil substrate tank. Again 4dKH solution...However, I can't comment on long-term consistency...at the moment...and maybe I should confirm the readings with another drop checker to make sure.

10644291073_7b66c14bf3_c.jpg
 
Seeing as CO2 is heavier than air, would it be a good idea to leave a small amount of space above the waterline so any CO2 released could sit on the surface of the water?
No, you are going to lose much more CO2 via diffusion into the air. Ideally you want bubbles that are as small as possible, with as longer retention time as possible in the water column.

cheers Darrel
 
No, you are going to lose much more CO2 via diffusion into the air. Ideally you want bubbles that are as small as possible, with as longer retention time as possible in the water column.

cheers Darrel

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.
 
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