Yeah, I think Mammoth is right too. The resivoir, your clear container needs to be light proof to prevent algae from growing in your water.
And I am not expert, but I dont think that your hydroton should be sitting in the water that way. As far as I have learned so far the pots are supposed to be elevated so that the bottoms are just above the surface of the water.
It seems to have been working for you this way though, so I could be wrong. Just thought I would give some input