replace light bulb induces cynobaterica??

[Navarchus]

I don’t know what the percentage of rocks you have add from the total weights of your rockery and if you cleaned them or cycled them but…..
Yep! That might be just it.
The introduction of dry rock to the system will cause the rise and build up of phosphate and nitrate (decomposing of dead animals in the rock into ammonia -> nitrite-> nitrate)
The cyano just loves these conditions.