replace light bulb induces cynobaterica??

[Navarchus]

I would siphon out the Cyanobacteria
People have a tendency to forget that the light is a source of energy. When you change the light bulbs with new one you put more energy to your system and that my have some side effects. In tome it will go away but as I said I would shut down all water movement it the max and siphon it out as part of a water change.

In the future cutting down the lighting hours and gradually returning to the normal times will help the system acclimate to the change.