Dosing baking soda as a CO2 substitute? - Page 3 - The Planted Tank Forum
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post #31 of 42 (permalink) Old 03-26-2020, 05:34 AM
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Calcium Carbonate is not 'almost insoluble', it can vary in solubility depending on the level of Carbonic acid present in the water.


A quarter teaspoonful of food grade CaCO3 powder will appear to not dissolve in water immediately but if there's enough dissolved CO2 in the water it will dissolve within a day or mores time.


The good thing about CACO3 is that it raises both the GH and KH per volume of solid and it isn't as strong an alkaline per weight as Sodium Bicarbonate. It's also a slower change to the pH.
Yep, add some peat or leaves to tank/change water to add humic and fulvic acid compounds and many elements will increase their bioavailability to plants substantially. Fulvic acids will even deliver nutrients right through the cell wall tissues of plant without plant even having to expend any energy to obtain it. Small amounts will handle it, you don’t have to Blackwater your tank to get this benefit. Just a barely yellow tint is all you need.

RO and tap water is completely devoid of humic and fulvic acids, add them in yourself. They also protect your fish from water change shock and are a natural bacteria/fungicide. There is absolutely zero down side to adding them to your change/tank water, there is not a aquatic ecosystem on the face of planet that does not contain these compounds in some amount. If you’ve got lots of wood in your tank it will produce all you need of these compounds, if you stringently vacuum substrate and tank has no woods, just rock and sand you’ll have to add them. They are a natural byproduct of decomposition.

Last edited by DaveKS; 03-26-2020 at 05:47 AM. Reason: Typo
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post #32 of 42 (permalink) Old 03-26-2020, 05:56 PM
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So there you are with your low tech aquarium and 2-3 ppm of co2 in the water. Plants can easily take that up. There might be zero in the water a couple hours after the lights come on, or say halfway through the photo period.
Are you sure CO2 levels can go to 0 or even drop appreciably in small aquariums with filters?

Do you have any examples of high fluctuations in pH in low tech tanks ph 5 - ph 10?
I have yet to see an aquarium that has parameters like a stagnant swamp or a low alkalinity lake.
Do you see any aquariums that look like this?



Star Lake Vermont (referenced in walstad's book) as a low alkalinity lake.
It is theoretically possible, just not very likely in hobbyist tanks.


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post #33 of 42 (permalink) Old 03-26-2020, 06:57 PM
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Are you sure CO2 levels can go to 0 or even drop appreciably in small aquariums with filters?

Do you have any examples of high fluctuations in pH in low tech tanks ph 5 - ph 10?
I have yet to see an aquarium that has parameters like a stagnant swamp or a low alkalinity lake.
Do you see any aquariums that look like this?



Star Lake Vermont (referenced in walstad's book) as a low alkalinity lake.
It is theoretically possible, just not very likely in hobbyist tanks.
Not sure I understand the question, or what PH or that pond in the picture has to do with It? Plant uptake can easily zero out 2-3 ppm of CO2 in an aquarium. Have I ever tested this personally with equipment sophisticated enough to read a ppm of CO2? No I havent


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post #34 of 42 (permalink) Old 03-26-2020, 07:51 PM
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Are you sure CO2 levels can go to 0 or even drop appreciably in small aquariums with filters?
Isn't that the base reason that Walstad promoted the Siesta period for low-tech dirt tanks? Co2 that was built up overnight would be depleted during a full day light cycle. By doing the seista period it allowed co2 levels to be built up again. The exact decline or increase isn't really that important. What is important is that it made more co2 available.


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post #35 of 42 (permalink) Old 03-26-2020, 08:54 PM
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Are you sure CO2 levels can go to 0 or even drop appreciably in small aquariums with filters?
Isn't that the base reason that Walstad promoted the Siesta period for low-tech dirt tanks? Co2 that was built up overnight would be depleted during a full day light cycle. By doing the seista period it allowed co2 levels to be built up again. The exact decline or increase isn't really that important. What is important is that it made more co2 available.
Yes and the chart I posted above literally shows this and backs you up.

Last edited by Ddrizzle; 03-27-2020 at 12:57 AM.
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post #36 of 42 (permalink) Old 03-31-2020, 12:38 AM
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Isn't that the base reason that Walstad promoted the Siesta period for low-tech dirt tanks? Co2 that was built up overnight would be depleted during a full day light cycle. By doing the seista period it allowed co2 levels to be built up again. The exact decline or increase isn't really that important. What is important is that it made more co2 available.
First the siesta was not to my knowledge proven effective.
Second, Walstad isn't that dirted, no water changes, and even the filter is optional? (aka all Natural....)

Walstad can promote whatever she likes, it is up to us whether we beleive what she has written or extrapolated is applicable to the tanks we discuss here. I certainly don't in this case.

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Not sure I understand the question, or what PH or that pond in the picture has to do with It? Plant uptake can easily zero out 2-3 ppm of CO2 in an aquarium. Have I ever tested this personally with equipment sophisticated enough to read a ppm of CO2? No I havent
That was the example from Walstad's book of a low alkalinity lake, it happens to be chock full of algae, phytoplankton, and plants that can use CO2. This lake allows CO2 to go to practically zero (ph ~10) and great fluctuations in pH due to low kh. It is so different from the conditions in our tanks I can just about disregard any conclusions drawn from studies on this lake as being applicable for hobbyist purposes.

It is my assertion that shallow(small) tanks never go to 0ppm CO2, there an equilibrium maintained with air CO2 concentration and thus the impact of Carbon uptake from Carbonates is negligible. I think this is an easy assertion with reasonable flow from a filter and surface mixing.

I still remember the debates with @Edward about pH decreasing 'dramatically' at night from all the CO2 plants were releasing. It has never happened to me or to him or anyone I spoke to who runs CO2 24/7. The same can be said about pH increasing dramatically during the day from depletion of CO2. I have never seen it in a hobbyist tank and would welcome someone with data who has.


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Last edited by cl3537; 03-31-2020 at 01:34 AM. Reason: ...
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post #37 of 42 (permalink) Old 03-31-2020, 01:32 AM
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As a final note, some plants have gone as far to avoid using bicarbonates directly by making the immediate area a lower ph (around 6) so that the bicarbonate reacts with calcium in the water to form co2 for the leaves to absorb. Obviously in this case, co2 would be more efficient for the plants. A plant that does this is Potamogeton lucens.
Please stop misquoting Walstad's book, nothing reacts with Calcium, there is no redox chemistry going on in the water, there is no Calcium (which is a metal) in the water.

The Calcium ions(Ca2+) present in water do not do any sort of reacting and they remain Ca2+ throughout. All Walstad was referring to was changes in pH can allow Bicarbonates which are soluble to precipate out as Calcium Carbonate (which is marginally soluble in neutral water) in more alkaline water.

You would be better off copy and pasting the whole paraphrah and citing the author rather than trying to sloppily paraphrase parts of her book, that leaves less room for misinterpretation.


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post #38 of 42 (permalink) Old 03-31-2020, 05:37 AM
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It is my assertion that shallow(small) tanks never go to 0ppm CO2, there an equilibrium maintained with air CO2 concentration and thus the impact of Carbon uptake from Carbonates is negligible. I think this is an easy assertion with reasonable flow from a filter and surface mixing..
This assertion is logical but it disregards plant uptake. That's what will take 2 ppm to zero because plants are using it faster than it can reabsorb from the atmosphere.

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I still remember the debates with @Edward about pH decreasing 'dramatically' at night from all the CO2 plants were releasing. It has never happened to me or to him or anyone I spoke to who runs CO2 24/7. The same can be said about pH increasing dramatically during the day from depletion of CO2. I have never seen it in a hobbyist tank and would welcome someone with data who has.
Plants do release some CO2 at night when they are in respiration mode but its a small amount compared to what they take in. I believe it is known as net carbon sink. And most studies on this involve terrestrial plants, where it varies a great deal according to the species type and also things like temperature. Hard to say to what degree it happens in our aquariums.

Ive never heard of a high tech's PH going up at night. Frankly it's not going to happen because there's a lot more in the water to degas than what the plants theoretically would release. If anything it would slow or reduce the rate of increase (PH) a little bit.

Now, it may drop at night if you run CO2 24/7. It amost certainly will. But that is mostly because the plants arent taking it in at night so naturally there will be more accumulating in the water. You could argue over how much is due to the plants releasing but it'd be hard to prove beyond saying it probably contributes a little bit

I dont see how it could happen in a low tech because the plants dont have any extra to begin with. Its all being used to grow. And the ppm we're talking about are so low to begin with I dont see how it would be enough to even notice. But Ive never paid that much attention to a low tech so could be wrong. That is just what seems logical to me.


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post #39 of 42 (permalink) Old 03-31-2020, 03:08 PM
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First the siesta was not to my knowledge proven effective.
Second, Walstad isn't that dirted, no water changes, and even the filter is optional? (aka all Natural....)

Walstad can promote whatever she likes, it is up to us whether we beleive what she has written or extrapolated is applicable to the tanks we discuss here. I certainly don't in this case.
Not sure what you mean "Walstad isn't that dirted" did you mean "is dirted". So you don't believe in a dirted/soil tank that the substrate would build some co2, get used by the plants (if mass is high) and then the siesta would shut down plant uptake, the co2 would build again (above the normal 2-3 ppm) and the plants would have more available with lights on. I know Walstad states this she has repetitive tests of this. Easy enough to do.

With that said I see no benefit in a siesta in low-tech inert or obviously hi-tech. Why shut down plants that conditions exist for them to grow optimally.


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post #40 of 42 (permalink) Old 03-31-2020, 03:59 PM
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With that said I see no benefit in a siesta in low-tech inert or obviously hi-tech. Why shut down plants that conditions exist for them to grow optimally.
When I first heard of putting a break in the photoperiod (decades ago), the idea was marketed toward fixing algae issues. The idea being that algae was a simpler life form that thrived from lots of light. Plants are more complex and able to snap to it and grow quicker so the siesta was to help plants out-compete the algae. Mind you this was chatter between a few guys at LFS's and got repeated, etc like so much advice in our hobby, probably no experiments run or fact checking, or even much anecdotal evidence, just a concept that got accepted and repeated. Sold as an algae bandaid. That's how I first heard about it anyway... But yeah, the biggest/ only? benefit I see from a siesta would be the owner's viewing pleasure, ie. tank takes a nap while you're at work, to maximize before and after work viewing with lights on. Neat concept for dirt/ Walstad style tanks tho...
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post #41 of 42 (permalink) Old 03-31-2020, 06:09 PM
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Not sure what you mean "Walstad isn't that dirted" did you mean "is dirted". So you don't believe in a dirted/soil tank that the substrate would build some co2, get used by the plants (if mass is high) and then the siesta would shut down plant uptake, the co2 would build again (above the normal 2-3 ppm) and the plants would have more available with lights on. I know Walstad states this she has repetitive tests of this. Easy enough to do.

With that said I see no benefit in a siesta in low-tech inert or obviously hi-tech. Why shut down plants that conditions exist for them to grow optimally.
I meant, Walstad tanks have soil substrate and are designed to be no maintenance much like a natural lake or pond. That is not what the OP is considering here.

I had a tank without a filter 30 years ago, in biology lab, it smelled awful, had snails all over the place, high density of overgrown but healthy plants and fish. When I think of Walstad I think of that tank. But that seems a far cry from what the OP was doing here.

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This assertion is logical but it disregards plant uptake. That's what will take 2 ppm to zero because plants are using it faster than it can reabsorb from the atmosphere.
I am not questioning plant absorption and release of CO2 during the photosynthesis cycle, that is not in dispute.

However the affinity of water for CO2 as you approach 0 ppm CO2 in the water would be very high. The concentration of CO2 in the air is much more than that in the water and if there was near zero in the water that would drive the Air/Water/CO2 equilibrium to dissolve more CO2 into the water. With an open top tank and reasonable flow you would need a lot of fast growing plants to overcome that gas exchange equilibrium. These are conditions unlikely in a low tech hobbyist tank with a filter and reasonable surface gas exchange.

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Now, it may drop at night if you run CO2 24/7. It amost certainly will. But that is mostly because the plants arent taking it in at night so naturally there will be more accumulating in the water. You could argue over how much is due to the plants releasing but it'd be hard to prove beyond saying it probably contributes a little bit
No it doesn't, I run CO2 24/7 and so does @Edward, and the fluctuations in pH in both of our tanks are negligible from day to night. You are underestimating the Air/Gas CO2 equilbrium which is maintained. I have enough off gassing and CO2 absorption from AIR in equilbirum that what the plants may absorb or release is negligible. My tank is only a 17G so it has better gas and surface mixing exchange than deeper tanks, but I beleive Edward's is much larger than mine.


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Last edited by Darkblade48; 04-04-2020 at 09:23 AM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #42 of 42 (permalink) Old 03-31-2020, 10:10 PM
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Well I can tel you 100% that PH does drop further at night if you leave the co2 running. Ive done it, both intentionally testing the waters for running it 24/7 and also from leaving it on by accident. Im not saying it will absolutely happen the same way in every tank. Of course it wont be the same. But your assertion that it wont happen period is wrong.

Idk about you but Edward I believe operates with pretty low levels of CO2 compared to what most high tech folks use. That probably has a lot to do with his observations.

Also things like surface agitation, or lack thereof, surface area + tank depth, how many plants and what kind, temperature, lots of variables are going to influence what happens.

Adding: Its an easy theory to test. Just leave the co2 running all night and see if the PH hasnt dropped another tenth or so by 3 am. Its not going to drop a whole point or anything. But that extra tenth can be 10-15 more ppm depending on how much you started with. I would also hazard a guess that most folks arent paying close enough attention or dont have the right tool to accurately notice an extra .1 or .05 drop. We arent talking about a huge drop. That drop has already happened. You're starting from an already low point from saturation, and the lower it goes from there the more each little increment means in ppm. So even a .05 drop is significant.


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