Help with brown algae film

[Jagermeister]

One of my sps seems to be getting "attacked" by a thin, brown algae. I've had this colony for about 2 years. Water parameters:

Calc= 430
Alk= 3.4
NH4, NO2, NO3 = 0
Phosphate= 0
Temp= 79
pH= 8.25

Has anyone experienced this before? I'm debating on whether to try a freshwater dip, iodine dip, or just start fragging the healthy parts.

Thanks

 

[Jagermeister]

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