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Intense light, CO2 limitation growth


14 Mar 2018
I want to share my observation of plant growth in intense light, CO2 limitation conditions. I have two planted bowls hanged by my west facing window. They are zero tech setups with no filter, aeration, heater or artificial light, but bright shade and afternoon sunlight. The light is intense which I measured to be around 50 PAR in bright shade and 600 PAR in direct sunlight. Without circulation and floaters blocking the surface, there is limited CO2 diffusion from atmospheric gas exchange. Indoor air has higher CO2 than outdoor air, specially in homes with gas heat and stove as mine, so lacking circulation is a significant loss of CO2. The only source of CO2 in my setup is respiration from snails, shrimp and micros. I estimated dissolved CO2 dropped to 0.2 ppm at the peak of sunlight with corresponding pH rise to 8.8 at kH4 water.

As I feed the shrimp lightly every other day and do 20% water change weekly with water from my high tech tank, there is no shortage of nutrients from second hand nutrients and food. With extremely high light, unlimited nutrients, but limited CO2, the substrate plants thrive with vibrant color but grow extremely slow. The Ludwigia, normally fast growing stem, has not been pruned for a year as if it were frozen in size. There was no algae except Clado and spirogyra which I removed physically every few weeks. The floaters, as expected, grow fast with no CO2 limitation and need to be thin out frequently.


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