Re: Why is direct sunlight to roots inhibitory to plant growth?

Hi, 

I think the problem is not only on light, also on other organisms in water. 
Some kinds of microorganisms such as green algae will grow in presence of 
light, and they grow very fast. In this process, they use oxigen and 
nitrogen in water, thus compete with your plants. As to the plant itself, to 
my current knowledge, the root will not be inhibited by light.

So I think you should change the plant in to untransparent container, and 
change the solution after a period of time. 

Good luck.