Debunked: CO2-Myth --- See tanks without carbon dioxide fertilization


Feeder Fish
MFK Member
Feb 10, 2022
A final comment on a very long and interesting thread and what I have read there. This is only my opinion - I may be wrong and must at all times have an open-mind.

My plants.
Although I believe every plant can be grown well underwater the natural way doesn't mean I can do it. 'Well' means healthy and in its prime - not some sickly specimen which is just surviving which is what I see in my tanks. They just grow slowly which I prefer. My local water, soils etc.. limit the species that will grow in my tanks - the whole point of this thread. Crypts hate my tanks and barely survive. But those that like my conditions thrive and don't need injection.

The wild and nature
I shouldn't use the term 'the wild' but say 'outside'. My source of observation of natives is private dams and other public places. All are artificial water bodies that contain natives, not natural waterways. I think the ducks spread them around? I have never actually seen lilaeopsis outside but I believe it is double the size in an outdoor setting. The reason I believe this is because the nursery where I buy my natives grows them in outdoor ponds that get direct sunlight all day long and I noticed when I bought them that they were twice the length and paler than lilaeopsis I am familiar with. They were lime-green and very tall not the shades of green I am accustomed to. Now my lilaeopsis is starting to resemble theirs. Its the reason I am believer in high light conditions in aquaria. I consider all of my tanks are under-lit and would like to give them more. They presently only get about 2 hours of direct sunlight a day.

More plants/less algae
I think both points of view are right. In a natural system (which is how I try to keep my tanks) where nutrients are effectively fixed at least in total (I don't use liquid fertilisers or add fish food) then the more plants you have the less algae. But I can imagine in a tank where nutrients are being controlled that this does not work that way maybe. The concept of fixed nutrients is the reason that nutrients and gases should not be thought the same with regard to Liebig. A gas is a different variable than a nutrient - even of the nutrient is variable as well. They are not the same. My tanks always start lightly planted with a lot of green filemntateous algae which is pretty harmless to plants (its a kind of plant itself) and gradually this algae dissappears. I never remove it as it is helping me as the plant establishes. All of the tanks I have shown above except the first two are quite young (6 months) and still establishing themselves. They will fill out much more.
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Goliath Tigerfish
MFK Member
Jan 19, 2007
Laguna Beach
While I do agree that keeping planted tanks can be done without C02, my best results have occurred while using it. I keep both high tech and low tech tanks, I challenge anyone to grow a dense carpet of monte carlo without compressed C02.



Feeder Fish
MFK Member
Feb 10, 2022
Great tank! I have some monte carlo so I might take up the challenge, but unfortunately it doesn't appear to like my conditions much - its alive but not thriving. If I do succeed I will post it here.

EDIT: by 'natural system' and fixed nutrients I am referring to my tanks - not outside. With ducks crapping and animals regularly dying in water bodies it may not be that simple out there.
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MFK Member
Jun 7, 2019
Southeast, Texas
I am not disagreeing with you. But when starting a planted tank you may need more to get it established.
Once you have the plants established, roots, foliage etc. they are able to pull more needed nutrients form the tank.
I recently converted an established 75g tank to a high tech planted tank and it has been a tough learning curve.
Plants melting, dying and I had quite a few different types of plants.
I started adding CO2 because my plants were dying and the tank was also being taken over with green hair algae.
I now have that under control thanks to the added CO2 and reduced hours of light.
Oh and lots of cleaning, trimming and vacuuming.
I am finally seeing healthy growth, but in the process I had to trim off over half the leaves that had died.
Now I see pearling and O2 streaming off plants everywhere when CO2 is being added.
I am just running 6 hours of light and 7 hours of CO2. The CO2 comes on 2 hours before the lights and off 1 hour before lights out.
Also I noticed you over time ended up with plants that do well in your tank.
There are many plants that do not need as much CO2 and light.

I also have a native planted tank 20g that just has 2 DollarTree 100 watt equivalent LED bulbs and no CO2.
That tank has been set up for 2 months.
It is now doing well, but many of the plants I originally planted in it died, so I now have plants that do well (well sort of) in my tank.

Here is my 75g tank with CO2. It is just 5 weeks old and recovering.

Here is my 20g Native planted tank, low tech.
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Canister Man
Staff member
Global Moderator
MFK Member
Aug 17, 2005
Great, thanks for sharing your experiences 👍


Redtail Catfish
MFK Member
Mar 30, 2020
Planted tanks are what really got me interested in keeping fish when I started getting serious almost 20yrs ago. I had not heard of Walstad but I did read about providing a dirt layer capped with soil. I have been heavily influenced by Takashi Amano and have his books. I also have made sure to add Christel Kasselmann's books to my library as well because of the more technical level of information available in them. Her books required me to have a dictionary on hand to translate the horticultural terms that hobby level books don't use.
My first planted tank was a 50B that had 3in of soil and 4-5in of 2mm sand. I grew Echinodorus amazonicus (amazon sword) only and they were growing out of the tank in a solid front to back, left to right jungle. I had a Coralife 36in double PC fixture and no CO2. I eventually upgraded to a 65g with a sump and added CO2 but I have never really noticed a difference in ability to grow plants that I enjoy. I currently have multiple planted tanks ranging from 29g up to 140g and soon to be a 220g.
No CO2 and no ferts. I have a magnolia tree that is constantly dropping leaves so I cut them up and use them as the only organic material under the sand. Only the 29g has any soil now.
This tank is my favorite scape but I disliked the bowfront so I took the tank down. This was early in its life.30g bowfront.jpg
The 29g has been running for 3yrs. I had dwarf sag that grew to the height of the tank and streamered across the surface. 29g_planted.jpg
60g cube running for just over a year before rescaping. I was only able to use half the plants in the cube. I added some to my other tanks and gave away some generous portions.60_cub.jpg
Houses my N. Splendens.
Eight 29g tanks each with plants.
Rack of plants.jpg
140g with 5 G. Tapajo redheads and 9 or 10 raphael cats


Feeder Fish
MFK Member
Feb 10, 2022
Below is my latest attempt at a low tech tank, about 30L. It is only week one so too early to say but the signs are very good. Got a bit of green water? trouble in week 2 but I think that is the lighting - too high.

I have had to revise my thinking about LIEBIG. Since experimenting with a deep sand bed DSB (Father Fish method) recently I have learnt that CO2 in fact comes from the dirt so my performance may be due to that. So I may be wrong on my statements about Liebig. Won't be the first time I have said or thought something stupid :).

The freshwater deep sand bed technique (1 inch of dirt, 2 inches of fine sand, Father Fish method) seems highly effective at growing plants in sand. Very impressed so far. It also acts as a highly effective biological filter I understand. I noticed a post above mentioning a deep substrate.

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