I see we didn't offer any more suggestions....
I have 2-24g nanocubes upstairs. One tank has cyano and one does not. The one thing that is different in them is bioload. There's no one thing that causes cyano, but a fancy dance of many factors.
Let's look at some of the things people offer as suggestions as to what causes it and compare it to my two "identical" tanks. The tank with the Frondosa has cyano, the one with the Sphex does not......
1) Water changes and general cleaning: Both need it.
2) Flow: Both good use more, there's great surface agitation however. (I've also had cyano dancing in the outflow of my pump and that's some pretty high flow).
3) Good algae: Frondosa tank has none. Sphex tank has cheato.
4) Light: One is closer to the window than the other. I do not use tank lights on either, unless I'm feeding at night.
5) Feeding: 100% of the food is eaten, unlike if you pour mysis in your tank (for example). They eat chucks of fish from a feeding stick. No waste.
6) Bioload: Frondoa is 7" and a big ole fish. The sphex is a juvie and about 3".
7) Age: Both tanks are the same age, set up at the same time.
The two things that are different are nutrient export (desirable algae) and bioload. So, in one tank, I put "in" more than I take "out".
The only way I've helped with cyano in the past is with hard maintenance. Not one water change, but many. Cleaning up the tank of it's detritus and lastly, when I've decreased the number or size of the fish, it went away. I think bioload is the fuel, but you need a match to set that fuel ablaze. Clean the tank like the Queen was coming to visit. Then you also have to keep it up after she leaves.
Yes, I'm a part of the crowd that doesn't dose antibiotics in my display tank. Antibiotics kill many more things than just the cyano. There is no "Cyano Only" antibiotic. Those dying things can increase your nutrient level and it throws your tank out of balance. It's like a little ecosystem. Girls will understand this.... antibiotics may cure the cough, but now you have a yeast infection you have to treat (sorry, I'm a nurse) and so on and so forth. At least try your darnest to solve it naturally and I believe that is to step up water changes and maintenance..... remove the fuel.