Cyanobacteria.

[Essjay]

Fishless cycling is a balancing act. On the one hand, the bacteria need ammonia, then nitrite to grow but on the other hand these harm fish so they need to be kept as low as possible. In the early stages of fish-in cycling the levels usually increase by the day after a water change, and any amount over zero will allow the colonies to increase in number. A bit extra or a lot extra doesn't matter as long as there's extra.

 

[Stan510]

Ben didn't mention if he had plants and plant lights- the brighter than normal lights- so I would think the easiest way to kill BGA for HIM,is too blackout the tank while going on "nutrient removal war" That means cleaning the prefilter and also very important since he has no plants- use those gravel washers on it to get the heavy much out. DO NOT remove all gravel and wash out. You don't want to kill the good guy bacteria in it..you want the excess muck out.
In my big tank? I try to vacuum where the muck settles most rather than the whole 8' x2' bottom. That and cleaning the prefilter often as I can, that alone seems to slow the BGA to spots instead of tank wide.
Heavy Fish feeding, and intense lights feed the BGA. I just read today a Florida city had to warn customers that BGA had returned early to the local lake they depend on for drinking water. They used some serious algaecides!

 

[Stan510]

I'm also trying to figure out why backyard ponds with Koi and Goldfish and full sun almost never see BGA. I've never had it in a pond come to think of it.

 

[Seb2502]

I’ve had Cyanobacteria cover all of my plants. I did a blackout for a day or two and it was all gone, never came back

 

[Stan510]

If you are running normal levels of light one treatment can do that to cyano. But for high light? Almost nothing is 100% permanent..but keeps it down to unseen. One thing that never works is remove by hand and or big water changes. You have to upgrade your filtering,lower the organics.
You never see BGA in those crystal clear streams in Florida,but it happens all over the country in mud bottom slow or standing waters in summers heat. BGA also likes warm.

 

[Stan510]

Interesting trivia for plant people: Cyanobacteria live in the Gunnera plant. That's the giant leaved primitive plant that goes back to the dinosaurs,and is in the Rhubarb family that has also naturalized in the UK.