I just did a water change on Friday, lights are only 4 months old. The flow seems to be ok. I do have a stringy brown algae in the tank that I have not been able to get rid of
Is anything nipping at them? My zoas were doing great untill I bought a Bellus angel. I watched as the angel was picking at them. After I got rid of the angel they were fine.
Could be they are being overgrown by the algae; examine them closely. If you see the algae growing on or over take a very soft toothbrush or your finger and try brushing/rubbing the algae off of them.
zoas dont like high levels of phosphates and react distressfully to them... a bit like the canary in the coal mines. the phos lvls could also be causing your other algae problem IME