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If the plants growth is CO2 limited and you increase CO2 in tank plants will grow more and use more nutrients.
If the plants growth is CO2 limited then they may get holes in leaves and other defects dependant on light levels
If plants are light limited increasing the tanks [CO2] would not change the nutrients use 'much' - but would change the plants internal mechanisms to use the extra CO2 so some maybe some change in nutrients.
Low [CO2] levels cause plant stems to elongate also
Not a expert either.
But increased co2 levels will mean the plant has to use less energy to get the co2. So will put this extra energy into increased growth. So I would say no the nutrient demand would not increase.
This is the reason increased co2 will grow plants better in lower light situations?
More CO2 needs more nutrients.
This is moderated by the lighting levels.
How much more is very difficult to say, because no one has data in their tanks regarding the CO2 concentration levels that the plants are actually seeing, however, if you are already dosing EI then you don't have to think about it and do not need to make any adjustments. EI covers everything from low to high.
If you are not dosing or are only dosing a small amounts such as in weak commercial products (which are typically 99% water) then you need to think about it.
I also think that too many variables play a role in giving an answer.
I once read (somewhere on this site) if you want to reduce the speed of growth it is better to reduce the ammount of CO2 than to use less nutrients.
Hence the question whether the amount of required nutrition of the plant is determined by the ppm of CO2 in the water.
Er no, this is the start of heading down the path of poor plant health, plants dying and algae moving in. Poor CO2 levels and distribution (for supplied light level) are responsible for 99% of the plant health issues we see on this forum.
The way to slow plant growth down is the 100% no argument necessary, the tried and tested method of USE LESS LIGHT. The whole plant biochemical CO2 and nutrients processing rate is driven by the amount of light energy the plant is getting.
Once you have less light you can back off the CO2 & nutrient levels (not sure why you would want to anyway) as the plant will be unable to process higher levels.
This was posted a while back which may shed some light on it, as suggested the lighting is the ultimate driving force behind everything, plants are only going to grow as fast as the light makes them or tries to until you hit a point where the light is driving them beyond their nutrient and co2 threshold at which problems begin. All with same amount of lighting 1. There's plenty of co2 but growth is limited by nutrients so slow growth and the possibility of deficiencies. 2. Lots of Nutrients and growth is limited to the co2 it can get its hands on so better growth but the possibility of running into co2 related issues. 3. Would be the E.I and 30ppm co2 with good circulation model although the light graphic would be slightly lower as EI is in excess.
The ideal when not dosing EI is to marry up the ferts with your particular light or go EI and be done with it. In the case of where people were saying "the amount of CO2 in the tank determines the plants demand for nutrients" I would suggest yes it would as limiting the growth using co2 would indeed you would need less nutrients but if the lighting is too high it wouldn't take long before it pushed you past the threshold of problems.
These days I aim for graphic 3 but with growth rate from graphic 1 You just need to make the yellow light graphic sit nicely on on top growth rate 1 I don't really have the time to be dealing with graphic 3 and I find the vast majority of plants will do fine with reasonable lighting but I'm more into healthy fish and plants. I prefer to spend more time enjoying gazing into the tank than working on it. There's enough complications in my life without bringing the hobby in as well.
More growth means more plantmass means more nutrients used. But one could argue that with EI levels there is no need to adjust as there should be plenty already.
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