What is this?

[ClearwaterReefer]

She is trying to scratch it off on rock and sand. I can't catch her. What can I treat? What is it???

 

[Qasimja]

i cant really see it can you possibly take more pictures under whiter lighting

 

[Jay Hemdal Verified Community Expert]

Hi, background info is really important, as well as @Qasimja said, clear pictures taken under white light. Here is a link to a file that describes the additional information we may need:

Some Helpful Hints When Posting or Responding to Threads in the Fish Disease Treatment and Diagnosis Section

Aquarium Fish Disease Problem Solving Determining the best course of action for a problem with your aquarium can be a difficult task. Even advanced aquarists will often need to seek the help of others for complicated or unique issues. Our intent here on Reef 2 Reef is to offer expert advice...

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Jay