Brown diatom in established tank

[proxy001]

Hello,

I have a bit of a curious situation.
My 180g has been established for years. I have not seen diatoms since I set the tank up.
Recently, I realize my radion g5 were bleaching corals so I drastically reduced the intensity and program. (went from radiant at 60% to AB+ at 35%, running about 9 hours photoperiod, same as always)
I also reduced phosphate and just did a water change. Phosphate are 0.1 and nitrate fairly low.
I am running a Chaeto reactor...

Coincidence or not, I am treating the tank for fish disease (Focus, Metroplex, Kanaplex)

What is the cause of the outbreak?? Lights too low?

Should I increase my lights back up a bit?

Thanks !

 

[Flippers4pups]

Introduction of dinoflagellates into a system is a guessing game, but in most cases it was introduced as a hitchhiker on coral, rock, sand or inverts such as snails. What causes it to explode in numbers is also a guessing game, but one thing is certainly clear that they proliferate when there is little in the way of microfauna and bacteria to out compete them.

Some need light, some don't.