You definitely need to be the hardworking sorts if you want to have riccia on rocks.
The reason why it will float up is because as the riccia grows, the underlying layers that are held down by the threads/meshes are blocked out from the light and dies off, causing the riccia to break free.
You have to trim it very regularly to make sure that the growth of the outer layer doesn't detriment the health of the underlying layers.
Studying the water chemistry and nutrients is a science.
Knowing what plants to get and how to use them is an art.
Aquascaping is a marriage of art and science, the logical and emotional.
-Calvin
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