# Suitable co2 level



## Spider Pig (17 Apr 2008)

Just reading an interesting article on tropica website: Co2 and light stimulate plant growth part 3 http://www.tropica.com/default.asp

It looks at the respective effects of co2 and light on plant growth (not suprising).

However they did an interesting experiment on growth rates of riccia: Table below. The percentages are growth rates per day.
http://www.tropica.com/catalog/images/articles/akvaristik/UK_CO2_tabel1_large.jpg

5400 lux is meant to correlate with a well lit planted aquarium. There is a 3x increase in growth upping the co2 to 6.6mg/l, but upping it further to 35 mg/l only increases growth by 1% compared to before. 

Why then is 30ppm the recommended level for co2 in the planted aquarium if it has such a minimal effect? Would it not be better to cut down the co2 for a bit to make it last longer?

The other question I had on my mind is whether 4hrs of 50w lighting will have the same effect as 8hrs of 25w lighting? Essentially is it intensity or duration of light that is more significant to growth rate?


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## ceg4048 (17 Apr 2008)

Hi,
    Different plants have different CO2 demands. The experiment was performed on Riccia only. Do you think these results can be extrapolated to Althernatera or to P. stelleta? Not really. The 30ppm rule of thumb is a compromise value that that more or less satisfy a majority of plants assuming the use of typical lighting. Can you measure the PAR value in your tank? Hardly. So you have no way of knowing how your tank compares. 

Additionally, it is not at all certain that a tank has 30ppm at any time because our measurement of it is so rudimentary. Further, since nutrient or gaseous concentrations in the tank are not homogeneous you can have 30ppm in one location of the tank and have 15ppm in another location within the same tank. Factors such as flow rates and flow geometry in a tank are never really certain and they have a significant affect on the actual availability of CO2/nutrients to any given specimen within the tank. Just try running your high light tank with 6.6ppm and see what the effects are. I assure you it won't be a pretty scene.

Photosynthesis is initiated and limited by the amount of light energy input. This translates to intensity. A certain number of light rays reacts with the chloroplast cells. If the intensity is insufficient to generate a sufficient number of chemical reactions then longer duration cannot make up for this. The plant respires and uses energy all the time. This energy expenditure must be balance by energy production. If the amount of energy consumed just equals the amount produced by photosynthesis then the plant will just barely hang on. In order to grow, food production must exceed respiration + food consumption. This is why the growth rates in a low tech tank are so low - the light energy is much lower even though the duration is the same.

Cheers,


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## Spider Pig (17 Apr 2008)

I am unfamiliar with the other examples of plants mentioned but I understand that riccia is a faster growing species. Surely co2 uptake is correlated with growth and so riccia would have higher co2 demands than most plants. The intensity given was said to be similar to a well lit planted aquarium but I can see how this would be variable in a home aquarium however the benefit to an aquarium of lower light would be less. From the results it is hard to extrapolate how much benefit there would be to one of higher light but it seems unlikely that it would be three times as bright as their "well lit" planted aquarium. 

The point about co2 distribution is noted. Unfortunately can't put it to the test yet but may have a go when set up in the future.

It would seem to be more efficient to run more intense lighting for shorter periods rather than weaker lighting for longer periods. Do you think this would enable such a tank to grow "high light" plants without a significantly greater risk of algae associated with high light set ups? (Assuming fertiliser dosing is adequate)


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## Spider Pig (17 Apr 2008)

Found a good explanation on the Barr report on EI dosing

"I suggest 30ppm of CO2, while a tank with 2 w/gal might be okay with 15-20ppm, many with power compact bulbs and reflectors need to have their CO2 levels higher, 20-30ppm range is optimal for the lighting period. This was found by adding more CO2 until there was no net gain in plant growth while keeping the nutrient and lighting levels consistent during the testing period. Research on three aquatic weeds showed that the plants will reach and carbon fixing maximum at around 30ppm of CO2 no matter what light intensity is used (Van et al 1976). The maximum CO2 level no matter what light set up you might have is about 30ppm for these three very fast growing weeds, which we can assume have higher CO2 needs/demand than slower growing aquarium plants subjected to less intense lighting than sunlight. While the needs of some plants might exceed some of these parameters, itâ€™s very unlikely that this will occur and Iâ€™ve found no evidence to support otherwise having grown close to 300 species of submersed freshwater aquatic macrophytes. The CO2 level is enough to support non limiting growth, just like PO4, NO3 and traces. So in a sense, CO2 is over dosed since it's an easier target to hit and measure. Adding more will not harm plants and is only limited by fish health and O2 levels."

Would be interesting to see a graph of co2 level versus growth rate to see where it starts to plateau out.


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## Aeropars (18 Apr 2008)

As an example of how easy riccia is to grow and how undemanding it is, i've had it pearling with no CO2 addition.


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## ceg4048 (18 Apr 2008)

Yes, that's what I mean. Each plant has a different efficiency and Riccia seems to be very efficient CO2 feeder. I would have done the test with the most difficult of plants, i.e, the ones that are known to suffer more acutely from poor CO2. If they are less efficient at CO2 uptake then perhaps a higher concentration is required. Until we can measure CO2 accurately 30ppm is kind of like the holy grail. I drive my dropchecker into the yellow but I just have mostly a few tetras. Fauna limit the amount of CO2 you can inject so you have to look at other means such as better flow/distribution.

Cheers,


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## GreenNeedle (18 Apr 2008)

Spider Pig said:
			
		

> It would seem to be more efficient to run more intense lighting for shorter periods rather than weaker lighting for longer periods. Do you think this would enable such a tank to grow "high light" plants without a significantly greater risk of algae associated with high light set ups? (Assuming fertiliser dosing is adequate)



This is why a lot of people use a 'noon burst'.  Its a satisfy all recipe where the long low light period is all most of the tank needs and then the 'noon burst' gives the high lights their requirement.

There is however a lot of disagreement in my mind on what are high lights and what are low lights because some high light plants grow very well in my low light tank whereas some low light plants don't.  I tend to think the light requirement is more for the shape you want the plants to grow into. Like if you want a carpet then the high lights keep a plant lower wheras if you have low lights over the same plant it will reach up for the sky a little.

Either way I just throw in plants to my tank without worrying what their reccomended lighting is and see if it works or not.  If it doesn't then I know for the future.  If it does then I can add it to my list of possibles.

Andy


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## Spider Pig (18 Apr 2008)

is there a time duration for the noon burst to be effective e.g. more than 4 hours?


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## ceg4048 (18 Apr 2008)

Any period of higher intensity will be effective assuming that during the period of higher intensity, nutrients and CO2 are adequate for that intensity level. It's not really an "either/or" issue. More time at higher intensity generates higher growth, less time generates less growth. As Andy points out "high light" plants are really a misnomer in that different colors and different growth rates are produced with higher lighting/CO2. I'm much more inclined to believe that the category should be renamed to "High CO2 plants". Glosso, for example is a classic plant where many hobbyists think that they can merely crank up the light intensity. In fact you don't really need such a high intensity but you do need more CO2.

Cheers,


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## tanker (20 Apr 2008)

Hi all,
i've been quite a failure at glosso, well actually at most plants. lately i realised that the main problem is adequate CO2 injection. i've boost up the CO2 rate for the past 4 days and things are beginning to improve largely. glosso starts to send out runners, and other stem plants are breathing like crazy. 
i think my light is considered high as its 32watts for about 26litres of water. can i know what is the sign of fish are getting stressed out by too high CO2? i had 2 bad experience in gassing all my fish to death (before i got my solenoid and timer for CO2). therefore i was quite reluctant to pump in more CO2. there was once i realised my cardinal tetras had white spots on their body, is that a sign of poisoning? at current, my CO2 is at the rate of 1bubble every 15sec. the bubble is quite big. unfortunately i dont use a drop checker yet.

i just got another timer yesterday to swithc CO2 on an hour earlier than light. and it is 8hrs of light, 8hrs of CO2. any advise?


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## Ed Seeley (20 Apr 2008)

I wouldn't mess around with the CO2 level too much until you get a drop checker.  There are loads available at very cheap prices from Ebay and online retailers.

Signs of CO2 stress in fish will usually manifest as the fish gasping at the surface or other signs of respiratory distress such as flaring gills and difficulty in breathing.  To be extra safe I'd turn your CO2 off at least half an hour before lights out as this will give a little time for any excees CO2 to gas off before the plants stop using it when the lights go off.

The white spots on the body could be a number of things depending on their size and number.  Can you describe them in more detail?  Or maybe start a thread on them in the 'Fish' section?


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