Out of curiosity, what salt do you use? I've had a feeling perhaps my salt isn't providing enough trace elements (have absolutely nothing I can base this on, just a feeling).FWIW
I have this light below hung over my refugium about 6 inches above water. Chaeto is growing quite well - tank is 6 weeks old. Skimmer is upstream in drain chamber - chaeto and mix of LR in fuge. Chaeto is not tumbling -- just hanging out and growing
https://www.amazon.com/Lemontec-Eff...id=1510080312&sr=8-16&keywords=grow+light+led