Here he is.
Is this the same tank with the plant/algae problems from before? Just wondering, I've forgotten anything we may have discussed then.
When the light intensity changes as dramatically as it did here when you went from two to one tube, in fact cutting the intensity in half, all plants are going to react. They are now being forced into a new balance.
Can you post a photo of the "diatoms?" I'm wondering if this is what I get on Pennywort and swords from the light, that looks like diatoms but does not come off, and is I think a form of brush/beard algae.
I would stay with the two tubes, but reduce the duration, as CO2 is likely going to be used up pretty quick. Remember that plants will photosynthesize to the max, i.e., as fast as they can, up to the limiting factor, so they will photosynthesize fast during the early hours and then slow down as CO2 becomes limited. And at this point, algae takes advantage. The trick is to find this point.