GHA in overflow

[Navarchus]

Hi
Personally I like my overflow box clean of anything. This is a crucial water pass that you don’t want to be blocked for any reason!

I would do the following:
Install 100 micron sock on the outlet in the sump.
Use a scraper and a clean Toothbrush to get rid of it !
The reason for using the sock is to prevent the GHA from spreading in your tank.
For local treatment I have also found Kent Marine poliox as a solution. Injecting directly the daily dose on the GHA after closing all water movement, help me to get rid of a GHA located underneath my golden tip purple acropora. Just be very careful with this stuff it is very strong oxidizer and should be used in an established system!