Rasta Zoanthid has brown spot but is still open?!

[jscott20]

Not the best picture but my rasta zoanthids have been doing great, new growth, large extensions, eating fine everything! But a brown spot has started appearing on the side. it doesn’t seem to be effecting it as they are still fully open. should i be concerned and how do i get rid of it or help?! Thank you!

 

[Bizzy bee reef]

Not the best picture but my rasta zoanthids have been doing great, new growth, large extensions, eating fine everything! But a brown spot has started appearing on the side. it doesn’t seem to be effecting it as they are still fully open. should i be concerned and how do i get rid of it or help?! Thank you!

That kinda looks like a Gatorade but I may be wrong. It may just be the brown diatom algae. Again may be wrong