I'm updating way too often to have anything useful to say, but I wanted to jot some ideas down regarding getting rotala to grow in an aesthetically pleasing manner. I'm going to be focusing on rotala rotundifolia "pink" because I have had it under all sorts of different conditions. It has the honor of being my favorite plant so I've kept it every tank I've owned so far.
I suppose first I should define what I consider to be the ideal growth form. This is from my low tech tank, with lean fertilization and a substrate of wom castings and osmocote capped with BDBS.
Notice the bright pink tips with a pleasant orange-pink color through the rest of the stem. The nodes are dense, regular, and evenly spaced and the leaves are uniform and healthy.
Compare this to the same plant in a medium-high light tank with injected CO2, EI fertilization, and the same substrate.
Notice how it stretches sideways, is a much paler yellow green color, and has wider spaced internodes. The same pattern is showing up in most recent tank, with the rotala "pink" on the left. This one still has high water column ferts due to leaching substrate, and nosebleed CO2 levels.
The fact that the low-tech, low light tank version has better color indicates to me that nitrate limitation is very important to develop reds in Rotala rotundifolia (not a new idea by any means). The main question I have is what is causing the long internodes and creeping rather than vertical growth pattern.
The creeping growth could be explained by the higher light, but the rotala is also planted more densely in the high-tech tanks so you would expect it to grow up to avoid competing with neighbors.
Internode length might be related to a few things. It could just be higher growth rate causing the greater internode length in the nutrients rich tanks. I think the color spectrum of the lights might also have something to do with it. On my low-tech tank the lights look to be around 7500-10000K. On the other tanks I lean more towards the red and yellow side of the spectrum to make the reds pop more. I read an article that suggests that light in the blue spectrum can INHIBIT vertical growth, thereby causing decreased internode length. I don't know if it's true but I'm going to try adding more cool light and blues to the spectrum to see what happens.
There are also chemicals called plant growth regulators (plant growth retardants or PGR's in this case) that can be used in hydroponics to slow or arrest vertical growth. Many of these are carcinogenic though so I'm not going to be the one to experiment with their effects on livestock.
My challenge is that I don't want to decrease CO2 or light since the other plants like it, but I still want that short spacing between nodes and reddish color. So I'm going to experiment with natural methods like topping, different fertilization regimes, and different light spectrums to try and see what helps. Any suggestions are appreciated
In the picture below, guess which side of the tank is closest to the window?
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