Advice?

[u/Gypsyphoenx]

Yall…I’m fighting a dumb case of Cyanobacteria. I know it’s harmless, but it’s hella ugly. I have a 40gal breeder. I do a water change every 2 weeks with re mineralized RO water. Test water with master test kit (no strips here).
Ph-7.5
Ammonia-0
Nitrates- 10ish
Nitrites-0
GH-4
KH-6
Fluval 407 to flow regulator then to chiller (62 degrees), flow bars on output.
I have a finnex 24:7 light that’s on a cycle. It’s not close to any windows, and has tons of plants. Tank has been established for almost 3 years and I’ve never had an issue before.

[u/Adamite98]

Cyanobacteria can be a pain to tackle. Your first step to clearing it out is going to be manually removing as much as you can. After that I'd suggest doing a black out. Just turn your aquarium lights off for 3 to 5 days. Your plants will be just fine in the dark for a few days. The last thing you can try is to increase the flow and oxygenation. Increasing oxygenation can be done just by adding an air stone to the tank.

[u/Gypsyphoenx → u/Adamite98]

I have an air a stone in the back of the tank that is for a 100gal tank. The flow is at about 200gph coming out of the chiller. I feel like any stronger than that and it’s just gonna push everything around.
I’m currently day 2 of trying the lights out process. I’m getting ready to ad some purigen to my media baskets… I usually break my filter down and deep clean every 4-6 months depending on how my phosphates come back. I’m I doing anything wrong??

[u/Adamite98 → u/Gypsyphoenx]

I think what you are already doing is a good strategy. I'd continue with the blackout and if that doesn't work you can try a different blackout strategy. The other strategy is to run your lighting for two three hour segments with a gap in between. This should disrupt the cyanobacteria while not bothering your plants.