There is nothing unusual about the way the algae is behaving. Both cyano
and diatom algae are quite photosynthetic and like anything that is, stretch's out when the light is abundant and recedes when it's gone.
Algaes of any kind need two primary things to survive, light and nutrient. Since this is a reef tank starving the algae of light would be counter productive to coral health. It would also be a shortlived solution since it will slow down the use of the nutrient and do nothing for it's elimination. The only thing you can do otherwise is starve it of nutrient. Diatom is mainly fed from silicates which would come in through the water source. I would definately suggest checking that.
is mainly fed through organic and inorganic PO4
. That can come in through many sources but primarily foods fed to the animals. Cyano
also has the ability to manufacture it's own nutrient to a small degree making it much harder to remove. Cyano
can process these nutrients so fast in fact that if you add foods it can easily sorb the nutrient so quickly the inorganic PO4
may never show up when testing. The best means to eliminate cyano
is through the use of non-aluminum based PO4
granular sponges. It will remove all forms of PO4
and then work on removing silicates thereby killing both problems. Eliminate the PO4
and you eliminate the algae.