Cannot get my chaeto to grow for the life of me!

[Tyfighter]

I would try removing the foz down and replacing the light with a grow bulb.
I started off using a par 30 led spotlight and it grew ok but I switched to a 50w grow led from Amazon and the stuff grows like crazy. All I have for flow is the water running through my sump so I don't thing that is your problem.
Also fluconazole treatments always kills my chaeto so if you have using it that may also be the problem.